It seems the controller on steamdeck on windows detects as such when steam or whatever companion program is not running. Although in this state. You can only right click or left click by pressing against the pad itself.

Although on Linux side. As far as i remembered, it's up to how kernel driver developer to map the device input into different class. It would be up to valve to decide what to do in this case.

> 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