I've tinkered around a bit and found that with another dongle that uses displayport everything works fine. Changing volume and brightness from the keyboard not having to fiddle with monitor menus is a godsend :)

The dongle that's having problems is a "Selore&S-Global USB-C HDMI + DP" if that's something you want to keep on file.

Thanks for the detailed response and all your work making the app possible!