Element one is the hosted managed matrix server and bridge service. You don’t run that at all (I mean, it’s open source, so you could run your own server if you wanted but that’s not what I’m suggesting here).
You connect to that using a Matrix client (an app for your phone in this case). There are many. Element is the one produced by the same company, it’s Electron based so should work on the L5 but probably not a great experience.
Fractal is the native GTK4 client for Gnome. It’s currently still in development so you need to build from source for arm but once it’s released it should be easy enough to install with flatpak or apt. (There was an older GTK3 version “stable” you can install from flatpak or apt but that does not support SSO sign on (which element one uses) and is being deprecated in favor of the rewrite).