I do use QoS on my router, but that’s not what I want: I want it explicitly on OS level. If that doesn’t prioritize in the first place, it’s one hop lost with bad/missing prioritization. In my example, my bad ping was actually with enabled router-prioritization. It’s not enough.

Thanks for the links, I’ll check them out!

Found the reason: You need to install mumble via rpm, not via Flatpak.

Now TTS works, but at a fantastically bad robotic voice. Need to figure out how to add other voices/better quality next.