Its probably the same or close to the default hardware mapping as the default SteamInput mode for a Deck, in Desktop mode, would be my guess, basically sans virtual keyboard as Steam does its own virtual keyboard via Steam/SteamInput.

Obviously works much better and fully featured with the SteamInput system, but it isn't a total brick if you don't have Steam.

Which yeah, _should_ mean that it would be possible to write a fully opensource kind of controller manager/bus type thing for it.