But is WSL1 supported by the POSIX layer? I don't think so. I think it uses some of the mechanisms built for the POSIX layer but I think it is a separate "personality".
Alright, let me be more clear: WSL1 is NOT the POSIX personality of Windows NT. The POSIX personality was very dumb and minimal. WSL1 is NOT that. It is a different thing. And the POSIX personality doesn't even exist anymore.