Interesting question. I remember M/S sold or spun off Xenix, but I thought that was due to them wanting to focus on DOS and Windows.

Found this and the answer is "no" :) Seems they rid of it due to Bell Labs breakup, see "Transfer of ownership to SCO":

https://en.wikipedia.org/wiki/Xenix

Yeah, it was before the bigger antitrust suits but IIRC it was part of what set the stage for them

How is Linux a Unix derivative apart from some guy in Finland reading a sysV syscall manual in 1990?

I don't think SCO's claim ever got adjudicated but it was enough to let them shake down multiple companies

IIRC SCO's claim was flawed as they didn't produce the infringing code and doubly flawed as they didn't even own the right to the Unix code.

Ahh yeah I remember that one now.

I mean Microsoft actually had a quite successful UNIX derivative named Xenix in the 80s (later sold to SCO).

Right, that was mentioned in the case IIRC; they didn't want that to happen again