React Native 0.82 iOS linker error: Undefined symbols for architecture arm64 (unsafeExecuteOnMainThreadSync )

Question

I’m migrating an existing React Native app to React Native 0.82.x. Android builds and runs fine, but iOS fails at the link step with the following error:

Undefined symbols for architecture arm64:
 "facebook::react::unsafeExecuteOnMainThreadSync(std::__1::function<void ()>)", referenced from:
 _RCTUnsafeExecuteOnMainQueueSync in React[118](RCTUtils.o)
 RCTUnsafeExecuteOnMainQueueOnceSync(long*, void () block_pointer) in React[118](RCTUtils.o)
 "facebook::react::executeSynchronouslyOnSameThread_CAN_DEADLOCK(std::__1::function<void (std::__1::function<void (facebook::jsi::Runtime&)>&&)> const&, std::__1::function<void (facebook::jsi::Runtime&)>&&)", referenced from:
 facebook::react::RuntimeScheduler_Legacy::executeNowOnTheSameThread(std::__1::function<void (facebook::jsi::Runtime&)>&&) in React_runtimescheduler[5](RuntimeScheduler_Legacy.o)
 facebook::react::RuntimeScheduler_Modern::executeNowOnTheSameThread(std::__1::function<void (facebook::jsi::Runtime&)>&&) in React_runtimescheduler[6](RuntimeScheduler_Modern.o)
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

So the compiler sees the declarations (headers) for these two functions, but the linker cannot find their implementations.

Environment

1. React Native: 0.82.x
2. iOS: platform iOS 16
3. Xcode: 26.0.1
4. CocoaPods: (latest)

Firebase:

• @react-native-firebase/app
• @react-native-firebase/auth
• @react-native-firebase/crashlytics
• @react-native-firebase/firestore
• @react-native-firebase/remote-config
• @react-native-firebase/analytics

Using New Architecture (RN 0.82)

Using Hermes

Using use_frameworks! :linkage => :static (required by React Native Firebase)

Android builds without any issues.

def node_require(script)
 # Resolve script with node to allow for hoisting
 require Pod::Executable.execute_command('node', ['-p',
 "require.resolve(
 '#{script}',
 {paths: [process.argv[1]]},
 )", __dir__]).strip
end
node_require('react-native/scripts/react_native_pods.rb')
node_require('react-native-permissions/scripts/setup.rb')
platform :ios, '16.0'
prepare_react_native_project!
# BUNU SİL (gerek yok, RN kendi ekliyor)
# pod 'React-RCTText', :path => '../node_modules/react-native/Libraries/Text', :modular_headers => true
setup_permissions([
 'LocationWhenInUse',
 'LocationAlways',
 'Camera',
 'Notifications',
 'Contacts',
 'PhotoLibrary',
 'PhotoLibraryAddOnly',
 'AppTrackingTransparency',
])
linkage = ENV['USE_FRAMEWORKS']
if linkage != nil
 Pod::UI.puts "Configuring Pod with #{linkage}ally linked Frameworks".green
 use_frameworks! :linkage => linkage.to_sym
else
 # RNFirebase dokümantasyonuna uygun zorunlu ayar
 use_frameworks! :linkage => :static
end
target 'CostaCoffee' do
 config = use_native_modules!
 # --- ÖNEMLİ KISIM: Firebase için modular headers ---
 # FirebaseAuth’ın bağımlılıkları
 pod 'FirebaseAuthInterop', :modular_headers => true
 pod 'FirebaseAppCheckInterop', :modular_headers => true
 pod 'FirebaseCore', :modular_headers => true
 pod 'FirebaseCoreExtension', :modular_headers => true
 pod 'GoogleUtilities', :modular_headers => true
 pod 'RecaptchaInterop', :modular_headers => true
 # Diğer hata verenler
 pod 'FirebaseCoreInternal', :modular_headers => true
 pod 'FirebaseCrashlytics', :modular_headers => true
 pod 'FirebaseFirestoreInternal', :modular_headers => true
 pod 'FirebaseABTesting', :modular_headers => true
 pod 'FirebaseInstallations', :modular_headers => true
 pod 'GoogleDataTransport', :modular_headers => true
 pod 'nanopb', :modular_headers => true
 pod 'FirebaseCoreExtension', :modular_headers => true
 # Eğer core’ları ayrı ayrı ekliyorsan (çoğu zaman gerek yok):
 # pod 'Firebase/Core'
 # pod 'Firebase/Auth'
 # pod 'Firebase/Crashlytics'
 # pod 'Firebase/RemoteConfig'
 # pod 'Firebase/Firestore'
 $RNFirebaseAsStaticFramework = true
 use_react_native!(
 :path => config[:reactNativePath],
 :app_path => "#{Pod::Config.instance.installation_root}/..",
 :fabric_enabled => true,
 :hermes_enabled => true,
 )
end
post_install do |installer|
 react_native_post_install(
 installer,
 '../node_modules/react-native', # veya config[:reactNativePath]’i yukarıda global yap
 :mac_catalyst_enabled => false,
 )
end

Note: pod install completes successfully. I used to see the "Swift pods cannot yet be integrated as static libraries" warnings for Firebase, but adding :modular_headers => true for the dependencies fixed that. Now pod install is clean and the only problem is this linker error on Xcode.