I use Fluffychat. Element is more up-to-date with features, but I think I like the simplicity and feel of Fluffy. Both are available via F-droid at least. There probably are other methods. And yes, both have Linux desktop and developer-hosted web-apps.
FYI Matrix is not an app, but a protocol. Like how you can use different clients to connect to Lemm-Lemm, you can use different apps for Matrix, and not every app has all features. Heck, even the sync authentication systems (that allow you to export your messages to different devices) are different!
But then there's the fact that you have manage your decryption keys on your own!
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I think Signal is better for video calls.
It's a bit less decentralized, but it's a lot simpler. A popular thing about Signal is that Edward Snowden talked about a Signal update in a congratulative tone of voice.