Things are so different now as compared to 20 years ago, if you go back and look at MF in its heyday. There was so much vibrant conversation there, the occasional trolling and flamewars aside. Today, I think a newer generation just isn't as into these longer-form online conversations. In terms of where I spend the most time, it's Twitter, although I mostly just read. My account there is private just for my own privacy reasons -- a couple of times I accidentally tweeted out stuff out from the wrong account and locking it down restricts that potential damage. I'll also look at IG and sometimes participate in domme's Q&As there. I hate OF. The platform is so clunky, and the conversations you wind up having are just chit chat or generic DS talk designed to keep you paying. (This has to do with the fact that you can't discuss in-person on OF, so nothing can lead to anything in the real world.)

I have a personal Reddit account but not a kink one. Would be interested in the subreddits you like.

I haven't tried SP but maybe should. I'll also use NF from time to time. The main domme I talk to there has turned into a bit more of a personal thing as most of our conversations/play now occur off that platform or via text.

One platform I would add is podcasts. In terms of time, I probably spend more time listening to kink podcasts than anything else, although, obviously, that is entirely one-way and not a conversation. But there's the Masocast (dormant much of the time but now Axe says he's recording more interviews), What Women and Other Wonderful Humans Want (terrible name but good guests and good questions if you can deal with the host's style), Damiana Chi has an occasional podcast. Erin Pimm has the Bedpost podcast. There was an interesting podcast last year called Good Pain, where two mostly vanilla, kink-curious people had some interesting guests on, including several dommes.

Also, speaking of Instagram, Mistresses Shayla Lange and Lola Jean do their online tutorials Seven Days of Domination, and even if you don't sign up there are hour-long conversations with each guest after.