There also is the empty https://kbin.social/m/WritingPrompts. On Beehaw’s writing some people have posted prompts and it’s the first place here where I’ve actually seen someone reply to a prompt. It’s not a dedicated writing prompt space though.

In general it looks like the migration is mostly spearheaded by tech rather than art, which I sort of expect. I mean the original /r/writingprompts didn’t even discuss or acknowledge the protest at all.