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
Well, this is kind of work in progress for XMPP and DeltaChat doesn’t support it. But you can for example try out https://movim.eu/ which is a webbased xmpp client (with PWA app) which does support screensharing in small group calls.
Matrix stans mentally block out the many issues it has, so take everything they say with a grain of salt 😅