So when we say "they abandoned posix compatibility", are we saying "They abandoned the POSIX filesystem storage backend"? I believe that's true, I used to use minio on a FreeBSD server but after an update I had to switch to just passing in zfs block devs.

Or are we saying that they no longer support running minio on POSIX systems at all, due to using linux specific syscalls or something else I'm not thinking of? I don't know whether they did this or not.

Those seem like two very different things to me, and when someone says "they don't support POSIX", I assume the latter

Ah, yes, I didn't even think of that. I always understood it as "abandon POSIX filesystems (as backend for S3)" because I knew about all these issues with filename/directory clashes,

I don'T think they would abandon POSIX systems in general, because what sense would that make?