Is it possible to use an external controller instead of using the mouse/keyboard in desktop mode ?

Yes of course

Yeah i use my controller in desktop mode. You can set the steam input profile in the steam settings on desktop mode.

Yes

https://steamcommunity.com/app/1675200/discussions/0/6126609705338539181/

Boot into Dekstop Mode, open the Gamepad configuration, with the controller connected, swap the order of the controllers so the 360 is the primary (or see if you can turn off the Deck controller) and set your configuration for desktop there.

It should work, it might think it’s player 2 though. In handheld mode there is a menu to change controller order, not sure where it’s at in desktop.

I'm really amazed that it works so well. Thanks everybody

Using SteamInput yeah, I’m pretty sure

It basically works the same as the Deck’s controls itself, you’d just have to configure it in Steam. Not sure if it would have a default config or not though

You should even be able to connect using BT assuming it’s a wireless controller.