We have just shipped an updated Steam Deck Client to the Preview/Beta channel.
General
The game launch progress screen screen will now show a note if the "Maximum Game Resolution" setting resulted in the game running at a resolution lower than the display's native resolution.
Moved the "Maximum Game Resolution" setting from Settings->Display->Advanced to Settings->Display.
"Maximum Game Resolution" options will now be generated based on the current display's aspect ratio. On non-standard aspect ratios, additional options will be available under 'More options'.