Q: Laptop via USB-C -> Sound-Settings -> Monitor

I’ve got an annoying problem with my Thinkpad L480
(Kubuntu 22.04 with plasmashell 5.24.7 and KDE Frameworks: 5.92.0).
The Laptop is connected via USB-C to my Eizo-Monitor which has a KVM-Switch inside.
Whenever I choose a sound or a video to play I can change the settings for the speaker here:

When I changed the source to “Digital Stereo (HDMI)” everything works well and the output device for the sound is now the monitor via USB-C.

But: This setting “is not stable at all”. I have to repeat these steps often … it can happen that I just switch to another browser tab and when I come back to the one with a video there’s no sound any more. I have to repeat the setting and set the output to “Digital Stereo (HDMI)” again. Then it works again…

I don’t know if this is a KDE-/Plasma-problem or what the problem could be. Maybe someone here with a brilliant idea?
Thank you.