Yeah, I joined Tumblr soon after it started in 2007 (back when you didn't even have to enter a birth year, which I noticed when Tumblr recently demanded that to show you all posts), then didn't do anything with it for years, but it came in handy to have my pseud when fandom moved there.

I have a Discord account, but don't really use it, because I find chat kind of stressful. And the organisational side seems kind of closed/clique-ish and hit-and-miss whether you find a niche with a group you like. That was already the case with fandom IRC rooms for The Sentinel in the late 90s. It would probably be a bit easier now, because my English has become fluent during my time in fandom, and also I'm typing a little faster now, but I like asynchronous interaction better.

I've recently seen mention of cohost.org but don't know anything about that project? company?