I have an OG Steam controller.

On Linux, whenever I connect to my computer without steam running, it will show up as a standard USB HID device. This means, funny enough, I can use the trackpads like a mouse n stuff on my desktop environment.

However, SDL3 (and SDL2 via sdl2-compat and SDL1 via sdl12-compat with sdl2-compat (lol)) supports the steam controller. This means that, without using steam, I get native gyro support and stuff in software like Ryujinb and Citron.

Furthermore, at least on linux, there is sc-controller which is a userland driver that makes the steam controller present itself as a standard Xbox controller. Of course, this means you aren't gonna be able to use the fancy features directly in the game, but it does mean for software that doesn't use SDL and isn't on steam directly, it will act as an FOSS alternative steam input layer. Also, it even has Cemuhook motion server. This mean before SDL3 added gyro support for the steam controller (giving any emulator using SDL3 and SDL2 via sdl2-compat gyro support native), you could have still used gyro controls. Also, with Proton now, I think there is a flag to tell Proton to use SDL input method instead of steam input. I think this means (i have to test it), that you can use SDL to use steam controller with proton outside of steam.

I think on windows, we will see something like sc-controller.