I’m experiencing the same issue — my apps stop working on iOS 16 and 17 when built with Xcode 16 (currently using 16.3).
The error message is the same:
Library not loaded: /System/Library/Frameworks/SwiftUICore.framework/SwiftUICore
I managed to work around the issue in one of my apps by marking the framework as optional using the linker flag -weak_framework SwiftUICore under the App Target > Linking > Other Linker Flags.
It would be great to get more information from Apple regarding this. Why are iOS 16 and 17 attempting to load a framework that’s only available in iOS 18? Am I missing something?