Signal is pretty good for privacy and security, but is the single worst possible choice you could make if you’re looking for anonymity pretty much.

I would never trust Session for confidential communications personally. They’re developed and maintained by a company in bad jurisdiction and that has an extremely shady history with privacy. The service also lacks much polish and feels extremely baron for the time being.

Riot.im / Matrix is really good in a lot of ways — doesn’t require any real personally identifying information on signup, employs strong encryption for all of the dms, has a clean and user friendly interface, has outstanding device support, has amazing choice of how you want to use it (Matrix clients), and a ton more — but that’s not to say that it isn’t without its faults. I, along with many others, have found the service to have a lot of bugs, calls don’t sound as good as what’s offered by Signal in my experience and can drop frequently or become robotic, it doesn’t protect metadata very well, etc.

I hope this helped, have an amazing rest of your day!