@vlagged, you missed XMPP (“Jabber”) with OMEMO, e.g. by Coversations client in an Android runtime environment.
As with Matrix and its clients, server and clients are verifiable, hence these two are the only solutions I would ever trust. But with XMPP it is a lot easier to run an own server, as there are two well established FOSS implementations (ejabberd and prosody) and XMPP servers are federated (like email servers) by default, hence one can use any running server to chat with users on any other server.
See also: XMPP | XMPP Software