Technology

Matrix (as a protocol) appears to be very strong end-to-end encryption and is federated/decentralized. It can do encrypted and unencrypted chats for any number of users, so it can replace discord (which is not at all private or secure) and do private 1:1 communications (which I'd say is the best use case for it). It also does not require a phone number like signal does (which is usually tied to your legal identity and can be used for geolocation).

I wouldn't trust any electron apps, which is the framework the official Matrix client, Element, is built on. It's fully open-source so there are other clients out there which may be better. Of course, the biggest weakness is probably going to be the OS/firmware of device you run it on.

Edit: The desktop element clients rely on electron (which is a webapp framework built on google chrome, which is spyware). If you're on android, the app also renders in chrome (which is spyware), but that matters a bit less because android itself is a massive pile of spyware. iOS is also spyware that openly just copies all your files to a server in the US where they are "scanned for very bad things", retained indefinitely and may be accessed by your favourite state agencies without warrant.