Systems such as Linux, MacOS and windows? All terribly broken and unusable. Seriously you need better sources or more experience. POSIX is alive and doing better than ever.

> Systems such as Linux, MacOS and windows?

Of them, only MacOS implements POSIX fully. Windows doesn't. Linux implements a subset.

Now we're splitting hairs, Linux is POSIX compliant, but not certified as certification costs money. Windows is also compliant through Linux subsystem. On Linux side there are also distributions which are POSIX certified which then makes Linux certified as well. It's just the windows, which also was certified at one point, early 1990s and air force. So that makes me right?

Linux is mostly compliant, which doesn't mean fully compliant (but there are distributions that are fully compliant).

Windows isn't compliant, and "compliant through WSL" doesn't really make it compliant.

So that makes me right. Your opinion may differ, of course.