Signal is open source but it’s hosted centrally. So you’re trusting their server.
Matrix is a protocol it’s not hosted anywhere. But the primary developer and host instance now called Element.
But it being created and initially bankrolled by an Israeli spyware company known for creating backdoors, and the lead devs still refusing to acknowledge that doesn’t inspire me much more confidence.
If you want privacy SimpleX seems like better option than Matrix.





For easy privacy the answer is Signal. If you want to put in effort then SimpleX or others seem better.
Matrix MIGHT be okay if you self host it, but I definitely wouldn’t trust the main Element hosted server. But the dev team sketches me out too hard so I’d just pick alternatives.