In my quest for a #Discord alternative for my gaming group, I'm going to toss #Matrix into the bin of "nope". It ticks most of the boxes, but holy fucking hell the constant nagging to revalidate every fucking login is not going to fly. None of my friends are going to tolerate that shit just to talk about #TTRPG scheduling, campaign planning, and general life events. Intensely user-hostile.
@SharpCheddarGoblin You might look at Discourse. This is basically forum software (has live chat but that's not the emphasis), which you can host yourself or pay someone else to. I'm very happy with it. See https://discussion.tekeli.li/ for an example. (For voice chat in games I use Jitsi, similarly self hostable or you can use the public instance free of charge.)
tekeli.li forums, including unofficial SU&SD discussion

Tabletop role-playing and board games

tekeli.li forums, including unofficial SU&SD discussion
@RogerBW I glanced at Discourse a bit ago, was a bit turned off on how AI-friendly the whole ecosystem was.
@SharpCheddarGoblin Fair. Certainly there is no difficulty at all in running it without any AI features - this isn't a matter of "clear the tickybox each time you upgrade", it's just "don't attach your own AI account to your instance". There's no built-in AI, just ways to hook it in.