Today’s beta Steam Deck client update adds a toggle in the Developer menu for safe mode when connecting to an external display. Enabling this will force the Deck to use a low resolution when it’s docked; this might help if the external display has issues.

An in-game crash has also been fixed with regards to Steam Input, and “the previous behavior of using stick deflection” has been restored, rather than “the capacitive sensor for Radial Menus that don’t have center buttons bound.”

See the patch notes on Steam.