[baq]

> You can only right click or left click by pressing against the pad itself

The original steam controller’s LT and RT work as mouse buttons in mouse mode, too. Source: have 3 steam controllers

[mmis1000]

There won't be 'mode' if neither steam or other 3rd software is running though. So it must default to one of control layout. Fortunately, controller on steamdeck does have enough button to fit both.