> No the controller works for any game, outside of steam, without steam launched.

Can you provide any evidence for this claim?

That's how it worked with the original controller, and how it works with the steam deck.

Like I said, it won't have all the modern features as it will be stuck on a MKB profile or a Xbox gamepad profile (or whatever you configure). But it will work

I still use the original steam controller, and I can tell you this is not true. If steam is not launched, the controller runs in a keyboard/mouse emulation mode and is not detected as a controller. This behavior is hardcoded in the firmware and cannot be changed.