As for macOS, and iOS, if Apple removed POSIX how many apps written in Objective-C and Swift (not UNIX cli tools ported from Linux) would actually be affected?
Very few, because those written in C and C++ ported from other platforms are most likely making use of ANSI C and C++ standards.
Using libc is not the same as POSIX.
https://developer.android.com/ndk/guides/stable_apis
https://developer.android.com/about/versions/nougat/android-...
https://android-developers.googleblog.com/2016/06/android-ch...
As for macOS, and iOS, if Apple removed POSIX how many apps written in Objective-C and Swift (not UNIX cli tools ported from Linux) would actually be affected?
Very few, because those written in C and C++ ported from other platforms are most likely making use of ANSI C and C++ standards.