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’m not a lawyer, but I believe that if the Lemmy instance’s ToS indicates where disputes will be resolved, and either the site owner resides there or is an LLC that is registered there, that you could sue Meta in that location.
Meta is big enough that they are most likely conducting business there (even if digitally) and you could also show that the harm suffered was suffered there.