That's cause you're using a distro like mint which is using older builds of stuff.

Get yourself a most recent plasma 6 Wayland setup with pipewire for audio. It even has rdp server now.

What's most likely happening is your user space app wants the newer API but you're running old builds from two years ago.

It will continue to degrade for you unless you fully switch to a Wayland DM.

Anything built on X11 is basically deprecated now and no one is building on it anymore.