I installed updates later yesterday, which included both a Steam client update and a Bazzite update, and the usual shortcuts in Steam game mode for changing brightness, Xbox + left stick up or down, are now changing volume instead, just like on desktop Steam and are listed as such when holding the Xbox button.
I tried rolling back Bazzite, but it’s still the same. Did something change with the latest Steam client update? Is there possibly some way to get the old functionality back?
I’m using Bazzite on a GPD Win 4, which has volume buttons, so I don’t need another way to change the volume.
I also booted up my Steam Deck on Steam OS to get the Steam client update, and it still has the brightness up/down shortcut.
EDIT: Some additional info: Just booted up the Steam Deck again to try an external controller (Xbox Core controller). Not sure what it used to do, but currently the button combos I mentioned above do also change the volume and not the screen brightness when used on the external controller, even though holding the Xbox button it indicates the button combo would change the screen brightness (unlike on Bazzite on my Win 4 where it lists the function that matches what it currently does). Might be something to report to Valve; I’ll just have to figure out where.