Comment by pjmlp

Android does not, use at your own peril as it is not part of the official APIs and will get your app terminated if you use unauthorized APIs.

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.