Stoat (formerly known as Revolt) is a selfhostable, FOSS replacement for discord [Group chats and voice channels you can join any time].
Cool new name, however not as easy to use in other languages.
Voice chat is stil not officialy implemented.
Self-hosting there. Apparently nothing to do for you if you had already hosted before the name change.
The Android app has unfortunately disappeared (not been updated) on F-droid.
Edit: added short description for clarification
It looks like polyproto doesn’t have any intent to implement voice chat or screen sharing?
i think for my purposes i’m fine with hosting that through a separate service, so instead of XMPP + mumble i would run polyproto + mumble (or some other voip solution, screen sharing seems to be a decent way away in mumble)
but (as i understand it), polyproto isn’t a chat protocol per se, but more a protocol for federated message authentication. as an application of this protocol, they’re building polyproto-chat, which is a chat protocol. in theory, one could then also build a polyproto-voice so you can use the same account for both chatting and voice calls. i still think this is pretty far away, considering how young polyproto is, which is why my current vision is chat and voice as two separate services (which i also prefer because i imagine it makes the technology simpler and hosting easier)