Matrix is a federated system, kinda like Lemmy. If you just use an existing instance that you trust, it's basically just another e2ee messenger. But many people host their own, and for that you need to a) have access to a server or VPS and b) have that server secured, i.e. configure firewalls, certificates, etc. It's not super hard, but takes some technical knowledge. Your non-technical friends can just use your instance, tho.

The benefit is that you control your data, not some external provider. From a pure security standpoint, however, there's not a lot of benefit over, say, Signal.

Of course, that's the infrastructure aspect of security. Other things, like having strong and varied passwords, no biometric logins (or only with 2fa), not sharing personal information about yourself or friends online, those obviously everyone needs to follow.