We're all with you!
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.
I've blocked their entire domain and I now I don't see their NSFW posts anymore.
Go to https://kbin.social/d/lemmynsfw.com (basically `/d/<domain you want to block>') and press the block icon on the sidebar. Yes you'll have to briefly look at their front page before you can block their content.
Well we are one of the largest instances out there with open signups...
I'm really going to miss /r/writingprompts, I've written a lot of stuff for them over the years. Sadly I don't see a replacement popping up here yet and their mods also didn't bother with the blackout protest.