

If you want a EU-based messenger I suggest Threema. The key-management aspect of it is kind of annoying, but it’s still leagues better than Matrix in terms of feature completenes, usability and just general polish.
Matrix in its current state is a toy for nerds who are ready to dive into the jankiness and can spare the time to fix their broken messenger every once in a while. Amd the best part is, Matrix itself isn’t even usable. It has no UI, it’s just the protocoll. So you need some third party app to be able to even use it. And not a single one of these apps implements all of the features of the protocoll.
I guess you’re out of luck then. I’m not aware of a single usable decentralized Messenger.
Slack kind of works I guess. (nvmd, Slack nowadays is cloud only) But other than that it’s just a bunch of hobby projects held together by enthusiasm and luck.