We had an encrypted chat for a bit before I realized it was completely pointless with literally everyone in it but one or two having entirely stock phones with in-built Ai and tracking mechanisms. We used XMPP.

Since it was for a Jellyfin server, it basically meant anyone on an unmodified Google or Apple phone was basically a door to a seach of that data from either company for the text logged into each chatroom by each user, and displayed. Unless everyone is secure, no one is.