With the upcoming support for Apple Silicon ARM simulators, App.framework (and add-to-app xcframework) needs a simulator ARM slice on ARM macOS. Universal (fat) App.framework can no longer contain architectures for both iphoneos and iphonesimulator since they need to be build against different SDKs, but they can no longer be lipod together (lipo complains both binaries contain arm64 and fails).

Primarily this is a problem when building the debug stub framework:

And in flutter build ios-framework that smush together plugin frameworks.

• Build App.framework directly to build directory #69699 Output App.framework to different iphoneos and iphonesimulator directories
• Compile snapshot_assembly with sdk root set in Xcode #69731 Refactor the build system to take either the iphoneos and iphonesimulator SDK from Xcode instead of trying to guess from the architectures (to stop assuming x86 == simulator). Use it for aot
• Build either iphoneos or iphonesimulator App.framework, not both #69840 Remove lipoing from debug stub framework step and only use the requested iphoneos or iphonesimulator SDK, not for both. Refactor flutter build ios-framework as needed.
• Deprecate build ios-framework --universal #69720 Deprecate flutter build ios-framework --universal
• Add to app prebuilt binaries as xcframeworks website#4956 Update add-to-app website docs to use xcframework
• Use xcframeworks in prebuilt add-to-app sample samples#582 Update add-to-app sample to use xcframework
• Remove --universal flag in "flutter build ios-framework" #69733 Remove flutter build ios-framework --universal
• Deprecate and replace build aot #49562 Deprecate flutter build aot
• Add the ARM architecture slice

Flutter.framework engine work tracked in #64502