I got distracted from my work so I made some Continuwuity propaganda. Continuwuity is a lightweights Matrix chat server that you can self-host pretty easily. Give it a try :3
It's not matrix-based, but: Haven. It's what I setup the... second? third? time discord had burned their users. The only thing missing for me is Xbox support, as several of my social circle are console gamers. But for pc users, it's got everything I need.