this is an interesting question i’ve had banging around in my mind since well before Reddit’s implosion (and Discord’s enshittification), but which seems really worth asking now.
you can’t blame Reddit and Discord or their imitators entirely for these going out of style, but they’ve sure put the dagger in a lot of remaining ones, and i kind of wonder if they’re just in an irreversible and terminal decline a la USENET. i can only name two or three i even consider checking anymore, and i’m not sure how sustainable any of those are long-term.
Whenever I look at forums these days it’s because I need to ask a very specific question that Reddit doesn’t have a big community for, for example I’m getting into building valve amps (tube amps across the Atlantic) and I’ve spent much more time lurking on the DiyAudio forum than Reddit for that purpose.
I think forums have the problem of search engines actually being spam delivery engines these days and also a lack of interoperability including a need to have fifty million different logins, all which have to be different since the probability of at least one getting compromised is basically 1 given enough browsing. I think the Fediverse certainly will help those two issues.