@wildbus8979 @Bahnd Yeah, XMPP checks all the boxes. That said, I don't know how well encrypted group chats (MUC) work with various clients.
Also, while message contents are encrypted, metadata is not. Self-hosting ameliorates that, but if your "self-hosting" involves a VPS or whatever hosted by a giant corporation, then that's something to be aware of.
@just_another_person @bluelion Eh, don't discount inertia. A lot of debian development channels are still active on IRC.