Microsoft has made such a mess of controller I/O that they were kind of forced to go with their jank translation layer made from scratch and running with their main product - it makes sense, especially built up piece by piece
Of course now that they've made controllers work properly, they'll use that work to support their own controller, and in particular enable features like analog triggers + gyro aiming + rumble (xinput can't do these simultaneously), extra buttons (xinput can't do this), and the trackpads (you guessed it).
And it is Windows, because on Linux the controller does work without Steam if you get the right drivers. It doesn't get the full features but it's functional as a gamepad, at least.
For the OG controller on Linux, it was/is possible to use third-party open source software like "sc-controller" to map the pads and rebind things the way Steam does, without needing Steam running.
I don't have any reason to believe that similar projects won't work for the new version.
SDL2 and SDL3 have steam controller support. Also, now that SDL2-Compat is a thing (alongside sdl12-compat), this means literally every game/software that uses SDL 1-3 for controllers on Linux (and windows too) should support the steam controllers.
Of course now that they've made controllers work properly, they'll use that work to support their own controller, and in particular enable features like analog triggers + gyro aiming + rumble (xinput can't do these simultaneously), extra buttons (xinput can't do this), and the trackpads (you guessed it).
And it is Windows, because on Linux the controller does work without Steam if you get the right drivers. It doesn't get the full features but it's functional as a gamepad, at least.