Dropsitenews published a list of websites Facebook uses to train its AI on. Multiple Lemmy instances are on the list as noticed by user BlueAEther
Hexbear is on there too. Also Facebook is very interested in people uploading their massive dongs to lemmynsfw.
Full article here.
Link to the full leaked list download: Meta leaked list pdf
I think it's safe to say that all of the LLMs have been training their systems on any site they can get their hands on for some time. That's why apps like Anubis exist trying to keep their crawlers from killing their bandwidth since LLM companies have decided to ignore robots.txt, copyrights, licenses, and other standard practices.