Run a self hosted forum or instance of whatever you like, and just only let people sign up if they are recommended by someone or can argue their way in, basically. xenforo and some add ons can do that, and I'm sure there's a few self hosted messaging apps like you mention but I'm not as familiar
IRC is small and niche enough to be a good place for more ephemeral discussion if you have a bouncer to stay connected for you. Chat on it tends to move slowly, and the userbase trends more towards actual nerds.
I do not think this is a technology problem.
I think it is a problem of how we changed: shorter attention spans, and a much larger volume of information to process.
Short forms win, long forms vanish, which is a tragedy in itself as good writing requires good understanding, and understanding is impossible without attention.
I'm in my 40s. I remember lcamtuf from pl.comp.security when I was just getting started playing with FreeBSD and other fun stuff.