The controller requires some sort of drivers to get out of lizard mode and work as a general controller (with remapping and everything). This has been known as it acts identically to Steam Deck and the OG Steam Controller.
If you want to use the controller without Steam being used (which, it's worth noting, you can add non-steam games to Steam to use the controller, or adjust the default desktop profile to be a normal controller), then you should be able to use SISR (formerly GloSC and GloSI): https://github.com/Alia5/SISR
Or, on Linux, use sc-controller: https://github.com/C0rn3j/sc-controller
The default mouse+keyboard layout the controller starts in before Steam takes over. I think they call it that as a play on the phrase "lizard brain"