I could never get voice and video to work with my xmpp server. Maybe its worth another try. Of course I would never do something ao retarded as use the central matrix server, but I always wondered about their directory service so I turned it off. No doubt their pwa still leaks data even if you always use a "homeserver", but the main feature I'm not willing to give up is video, screenshare and voice calls. If you were in charge of a development team and the tools they use, how would you solve this problem given that e2e MUCs witg omemo are a central component of your use-case? 

 I don't know.  I'm not personally interested in voice and video.  I just want to get group chat off of Telegram. 

 I know there is the jingle protocol (sip over xmpp) but i never got it to work and i'd want a desktop client that can also screenshare