Matrix support with end-to-end encryption is now available in #Chatty on the #Librem5 by @purism
https://puri.sm/posts/how-to-setup-encrypted-chat-on-librem-devices/
Does it work for you?
I'm trying, but so far I get stuck at some problem when it tries to reach the homeserver: https://source.puri.sm/Librem5/chatty/-/issues/755