Element

Element is a Matrix server implementation and there is also a client maintained by the same people.

Also see https://element.io.

Start client automatically and minimized in KDE

Since the startup options in Element don't work in KDE, you may have to create an autostart entry manually.

To start the Flatpak version of the Element client minimized use the following arguments:

run --branch=stable --arch=x86_64 --command=/app/bin/element --file-forwarding im.riot.Riot @@u --hidden %U @@