Sorry,but have you at least read the wikipedia article before writing this post?

Matrix is a standard. Not an App. Just like Lemmy is.

There are dozens of clients (Element, Schildichat, Fuzzychat, Beeper) available to download for basically every system imaginable and in all major Appstores.

You can easily join an existing instance - and with beeper there is even one existing that handles all the bridges for you.

Only when you self-host it gets more tricky-just like it does with Lemmy(as a matter of fact Matrix is far easier to selfhost than Lemmy). And again there are various distributions available. They aren’t as easy as the clients and not as easy as flatpacks, but someone who has done their due diligence can absolutely handle them easily. (And self-hosting should absolutely not be “as easy as flatpacks/snaps” - the risk for both the admin and the net itself is too high). But again: The average user has little incentive to selfhost. Just like you don’t selfhost your Lemmy instance.

The Matrix environment is as easy to use as Signal, Threema, WhatsApp for ages now. In some points I would even argue that it’s more user friendly than Signal,btw.