Most of the alternatives mentioned have such low adoption that they aren't truly viable options yet - no matter how much we wish otherwise.
And I say that not as a critic - I actually use Matrix, XMPP, and Jitsi myself. But guess how many of my friends, family, or colleagues are on them?
Exactly.
That’s why I recommend Signal. At least there, people are likely to find folks they already know.
https://blog.cryptographyengineering.com/2024/08/25/telegram-is-not-really-an-encrypted-messaging-app/
To get encryption one must start a "secret chat". It's an opt-in! Regular users will not even know the option exists, that's how well hidden it is.
Regular chats? Plainly readable on the server.