I use Firebase in my Unity Project windows version, buided on iOS version, they give me this error (it's my first time with Firebase).
Using Builder v.3.73.2 and iOS 18.4 SDK
Building the dependency project UnityFramework...
+ Preparing output directory...
+ XCFrameworks: 0 supplied
+ Libraries: 9 supplied, 9 built
+ Frameworks: 0 supplied, 0 built
+ Pre-parsing project files...
+ Building UnityFramework for iphoneos (configuration: Release)
+ [arm64] Dummy.swift.obj is up to date
+ [arm64] .\Classes\UI\UnityViewControllerBase+visionOS.mm.obj is up to date
+ [arm64] .\Classes\Unity\UnityWebRequest.mm.obj is up to date
+ [arm64] .\Libraries\Il2CppOptions.cpp.obj is up to date
+ [arm64] .\Classes\Unity\CMVideoSampling.mm.obj is up to date
+ [arm64] .\Classes\UI\UnityView+iOS.mm.obj is up to date
+ [arm64] .\Classes\PluginBase\AppDelegateListener.mm.obj is up to date
+ [arm64] .\Classes\UI\UnityViewControllerBase+tvOS.mm.obj is up to date
+ [arm64] .\Classes\UI\UnityView+Keyboard.mm.obj is up to date
+ [arm64] .\Classes\Unity\UnityReplayKit.mm.obj is up to date
+ [arm64] .\Classes\UI\UnityView+tvOS.mm.obj is up to date
+ [arm64] .\Classes\UI\UnityViewControllerBase.mm.obj is up to date
+ [arm64] .\Classes\Unity\UnityReplayKit_Scripting.mm.obj is up to date
+ [arm64] .\Classes\UI\UnityAppController+ViewHandling.mm.obj is up to date
+ [arm64] .\Classes\Unity\CVTextureCache.mm.obj is up to date
+ [arm64] .\Classes\Unity\DisplayManager.mm.obj is up to date
+ [arm64] .\Classes\Unity\VideoPlayer.mm.obj is up to date
+ [arm64] .\Classes\Unity\DeviceSettings.mm.obj is up to date
+ [arm64] .\Classes\Unity\FullScreenVideoPlayer.mm.obj is up to date
+ [arm64] .\Classes\Unity\InternalProfiler.cpp.obj is up to date
+ [arm64] .\Classes\UI\StoreReview.m.obj is up to date
+ [arm64] .\Classes\UI\OrientationSupport.mm.obj is up to date
+ [arm64] .\Classes\PluginBase\RenderPluginDelegate.mm.obj is up to date
+ [arm64] .\Classes\UnityAppController.mm.obj is up to date
+ [arm64] .\Classes\Unity\AVCapture.mm.obj is up to date
+ [arm64] .\Classes\Unity\NoGraphicsHelper.mm.obj is up to date
+ [arm64] .\Classes\iPhone_Sensors.mm.obj is up to date
+ [arm64] .\Classes\Unity\Filesystem.mm.obj is up to date
+ [arm64] .\Classes\UI\UnityView.mm.obj is up to date
+ [arm64] Classes\main.mm.obj is up to date
+ [arm64] .\Classes\Unity\OnDemandResources.mm.obj is up to date
+ [arm64] .\Classes\UnityAppController+Rendering.mm.obj is up to date
+ [arm64] .\Classes\UI\Keyboard.mm.obj is up to date
+ [arm64] .\Classes\CrashReporter.mm.obj is up to date
+ [arm64] .\Libraries\RegisterFeatures.cpp.obj is up to date
+ [arm64] .\Classes\UI\UnityViewControllerBase+iOS.mm.obj is up to date
+ [arm64] .\Classes\UnityAppController+UnityInterface.mm.obj is up to date
+ [arm64] .\Classes\Unity\CameraCapture.mm.obj is up to date
+ [arm64] .\Classes\PluginBase\UnityViewControllerListener.mm.obj is up to date
+ [arm64] .\Classes\PluginBase\LifeCycleListener.mm.obj is up to date
+ [arm64] .\Classes\UI\ActivityIndicator.mm.obj is up to date
+ [arm64] .\Classes\Unity\MetalHelper.mm.obj is up to date
+ [arm64] Libraries\com.unity.mobile.notifications\Runtime\iOS\Plugins\UnityNotificationLifeCycleManager.mm.obj is up to date
+ [arm64] Libraries\com.unity.mobile.notifications\Runtime\iOS\Plugins\UnityNotificationData.m.obj is up to date
+ [arm64] Libraries\com.unity.inputsystem\InputSystem\Plugins\iOS\iOSStepCounter.mm.obj is up to date
+ [arm64] Libraries\com.unity.mobile.notifications\Runtime\iOS\Plugins\UnityNotificationWrapper.m.obj is up to date
+ [arm64] Libraries\com.unity.mobile.notifications\Runtime\iOS\Plugins\UnityNotificationManager.m.obj is up to date
+ [arm64] Including Libraries\libiPhone-lib.a...
+ [arm64] Including .\libGameAssembly.a...
+ [arm64] Including Libraries\Plugins\iOS\Firebase\libFirebaseCppDatabase.a...
+ [arm64] Including Libraries\Plugins\iOS\Firebase\libFirebaseCppStorage.a...
+ [arm64] Including Libraries\Plugins\iOS\Firebase\libFirebaseCppApp.a...
+ [arm64] Including Libraries\Plugins\iOS\Firebase\libFirebaseCppAuth.a...
+ [arm64] Including Libraries\Plugins\iOS\Firebase\libFirebaseCppFirestore.a...
+ [arm64] Including Libraries\baselib.a...
+ [arm64] Linking UnityFramework...
ld64.lld: error: undefined symbol: OBJC_CLASS_$_FIROptions
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppApp.a(app_ios.mm.o):(symbol ltmp5+0x0)
ld64.lld: error: undefined symbol: OBJC_CLASS_$_FIRApp
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppApp.a(app_ios.mm.o):(symbol OBJC_CLASSLIST_REFERENCES_$_.4+0x0)
ld64.lld: error: undefined symbol: OBJC_CLASS_$_FIRConfiguration
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppApp.a(app_ios.mm.o):(symbol OBJC_CLASSLIST_REFERENCES_$_.6+0x0)
ld64.lld: error: undefined symbol: OBJC_CLASS_$_FIRStorageMetadata
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppStorage.a(metadata_ios.mm.o):(symbol ltmp6+0x0)
ld64.lld: error: undefined symbol: OBJC_CLASS_$_FIRStorage
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppStorage.a(storage_ios.mm.o):(symbol ltmp5+0x0)
ld64.lld: error: undefined symbol: firebase::firestore::api::operator==(firebase::firestore::api::DocumentChange const&, firebase::firestore::api::DocumentChange const&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(document_change_main.cc.o):(symbol firebase::firestore::operator==(firebase::firestore::DocumentChangeInternal const&, firebase::firestore::DocumentChangeInternal const&)+0x1c)
ld64.lld: error: undefined symbol: firebase::firestore::util::internal::FailAssertion(char const*, char const*, int, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&, char const*)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(document_change.cc.o):(symbol firebase::firestore::DocumentChange::DocumentChange(firebase::firestore::DocumentChangeInternal*)+0x78)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_snapshot.cc.o):(symbol firebase::firestore::AggregateQuerySnapshot::AggregateQuerySnapshot(firebase::firestore::AggregateQuerySnapshotInternal*)+0x78)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_main.cc.o):(symbol firebase::firestore::Promise<firebase::firestore::AggregateQuerySnapshot>::SetError(firebase::firestore::util::Status const&)+0x64)
>>> referenced 42 more times
ld64.lld: error: undefined symbol: firebase::firestore::api::DocumentChange::Hash() const
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(document_change.cc.o):(symbol firebase::firestore::DocumentChangeInternal::Hash() const+0x14)
ld64.lld: error: undefined symbol: firebase::firestore::api::operator==(firebase::firestore::api::AggregateQuery const&, firebase::firestore::api::AggregateQuery const&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_snapshot_main.cc.o):(symbol firebase::firestore::operator==(firebase::firestore::AggregateQuerySnapshotInternal const&, firebase::firestore::AggregateQuerySnapshotInternal const&)+0x1c)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_main.cc.o):(symbol firebase::firestore::operator==(firebase::firestore::AggregateQueryInternal const&, firebase::firestore::AggregateQueryInternal const&)+0x1c)
ld64.lld: error: undefined symbol: firebase::firestore::api::Query::Hash() const
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_snapshot.cc.o):(symbol firebase::firestore::AggregateQuerySnapshotInternal::Hash() const+0x1c)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query.cc.o):(symbol firebase::firestore::AggregateQueryInternal::Hash() const+0x18)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(query.cc.o):(symbol firebase::firestore::QueryInternal::Hash() const+0x18)
ld64.lld: error: undefined symbol: firebase::firestore::api::AggregateQuery::Get(std::__1::function<void (firebase::firestore::util::StatusOr<long long> const&)>&&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_main.cc.o):(symbol firebase::firestore::AggregateQueryInternal::Get(firebase::firestore::AggregateSource)+0xa4)
ld64.lld: error: undefined symbol: firebase::firestore::util::internal::FailAssertion(char const*, char const*, int, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_main.cc.o):(symbol firebase::firestore::PromiseFactory<firebase::firestore::AggregateQueryInternal::AsyncApis>::PromiseFactory(firebase::CleanupNotifier*, firebase::FutureManager*)+0x138)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_main.cc.o):(symbol firebase::firestore::PromiseFactory<firebase::firestore::AggregateQueryInternal::AsyncApis>::PromiseFactory(firebase::CleanupNotifier*, firebase::FutureManager*)+0x84)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_main.cc.o):(symbol firebase::firestore::Promise<firebase::firestore::AggregateQuerySnapshot>::Promise(firebase::CleanupNotifier*, firebase::ReferenceCountedFutureImpl*, int)+0x13c)
>>> referenced 33 more times
ld64.lld: error: undefined symbol: firebase::firestore::util::internal_statusor::Helper::Crash(firebase::firestore::util::Status const&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query_main.cc.o):(symbol firebase::firestore::util::internal_statusor::StatusOrData<long long>::EnsureOk() const+0x28)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(transaction_main.cc.o):(symbol firebase::firestore::util::internal_statusor::StatusOrData<std::__1::vector<firebase::firestore::model::Document, std::__1::allocator<firebase::firestore::model::Document>>>::EnsureOk() const+0x28)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(transaction_main.cc.o):(symbol firebase::firestore::util::internal_statusor::StatusOrData<firebase::firestore::DocumentSnapshot>::EnsureOk() const+0x28)
>>> referenced 2 more times
ld64.lld: error: undefined symbol: vtable for firebase::firestore::api::AggregateQuery
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query.cc.o):(symbol firebase::firestore::api::AggregateQuery::AggregateQuery(firebase::firestore::api::AggregateQuery const&)+0x10)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(aggregate_query.cc.o):(symbol firebase::firestore::api::AggregateQuery::AggregateQuery(firebase::firestore::api::AggregateQuery const&)+0xc)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(query_main.cc.o):(symbol firebase::firestore::api::AggregateQuery::~AggregateQuery()+0x10)
>>> referenced 1 more times
ld64.lld: error: undefined symbol: firebase::firestore::model::FieldPath::KeyFieldPath()
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(field_path.cc.o):(symbol firebase::firestore::FieldPath::DocumentId()+0x20)
ld64.lld: error: undefined symbol: firebase::firestore::model::FieldPath::ValidateSegments(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>> const&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(field_path.cc.o):(symbol firebase::firestore::model::FieldPath::FromSegments(std::__1::vector<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>>&&)+0x1c)
ld64.lld: error: undefined symbol: firebase::firestore::model::FieldPath::FromDotSeparatedString(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(field_path.cc.o):(symbol firebase::firestore::FieldPath::FromDotSeparatedString(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)+0x2c)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(user_data_converter_main.cc.o):(symbol firebase::firestore::UserDataConverter::ParseUpdateData(std::__1::unordered_map<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, firebase::firestore::FieldValue, std::__1::hash<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>, std::__1::equal_to<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>, std::__1::allocator<std::__1::pair<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const, firebase::firestore::FieldValue>>> const&) const+0xac)
ld64.lld: error: undefined symbol: firebase::firestore::model::FieldPath::CanonicalString() const
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(field_path.cc.o):(symbol firebase::firestore::FieldPath::ToString() const+0x54)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(user_data_converter_main.cc.o):(symbol firebase::firestore::(anonymous namespace)::CreateFieldMask(firebase::firestore::core::ParseAccumulator const&, std::__1::unordered_set<firebase::firestore::FieldPath, std::__1::hash<firebase::firestore::FieldPath>, std::__1::equal_to<firebase::firestore::FieldPath>, std::__1::allocator<firebase::firestore::FieldPath>> const&)+0xcc)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(query_main.cc.o):(symbol firebase::firestore::QueryInternal::ToBound(firebase::firestore::QueryInternal::BoundPosition, firebase::firestore::DocumentSnapshot const&) const+0x400)
>>> referenced 1 more times
ld64.lld: error: undefined symbol: firebase::firestore::util::Throw(firebase::firestore::util::ExceptionType, char const*, char const*, int, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(exception_common.cc.o):(symbol firebase::firestore::SimpleThrowInvalidArgument(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)+0x24)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(exception_common.cc.o):(symbol firebase::firestore::SimpleThrowIllegalState(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)+0x24)
ld64.lld: error: undefined symbol: firebase::firestore::nanopb::MakeBytesArray(void const*, unsigned long)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(field_value_main.cc.o):(symbol firebase::firestore::FieldValueInternal::FieldValueInternal(unsigned char const*, unsigned long)+0x9c)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(user_data_converter_main.cc.o):(symbol firebase::firestore::UserDataConverter::ParseScalar(firebase::firestore::FieldValue const&, firebase::firestore::core::ParseContext&&) const+0x368)
>>> referenced by F:/Unity/Unity Projects/siponto-migranti/Siponto-Migranti/ios/Libraries/Plugins/iOS/Firebase\libFirebaseCppFirestore.a(user_data_converter_main.cc.o):(symbol firebase::firestore::nanopb::MakeBytesArray(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&)+0x2c)
ld64.lld: error: too many errors emitted, stopping now (use --error-limit=0 to see all errors)
Premere un tasto per continuare . . .