Briar, Matrix, Cwtch, Signal, Session, there are many, but which one is the best? I want to protect my privacy and I want my private messages to never be seen or recovered by anyone.
That might be hard, you know, because of screenshots.
I am not at all a pro on this, but if you look at the track record of some of these options you might be able to come to a conclusion. Signal, for example, has been subpoenaed a number of times and likes to repeat that they know about first and last connection, and that's it. But, Signal uses a phone number for registration, so some people might be put off by that.
Matrix is used by some government bodies (in France, I beleive), but you might want to host your own server (I don't know if admins have access to messages or not).
Briar "doesn't rely on a central server - messages are synchronized directly between the users' devices." [1]
Cwtch is one I've never heard of, but I like the buzzwords mashup of "decentralised P2P Tor Onion routing metadata resistant"
Session also proposes variation on that theme, and doesn't ask for a phone number.
I feel like this is a tough question that is up for debate.
Session
SimpleX Chat
Anything that requires personal info is right out in my opinion. The above 3 do not.