I think if you put your device's VID/PID into SDL_GAMECONTROLLER_IGNORE_DEVICES, it will work. For example SDL_GAMECONTROLLER_IGNORE_DEVICES=0xABCD/0xDEF0. However I haven't really tested this usecase, and the Steam client itself mucks with this variable for its controller configuration support, so I'm not sure how that will behave.
Another option would be to add a Steam controller configuration mapping for your device, with no mapped outputs.
Feature Request
I confirm:
contain this feature already.
Description
I have been using Antimicro to do some custom controller mapping and scripting in certain games, and what bothers me is that Steam can not be told to ignore a certain controller I have plugged in. I used to get around this by unplugging a controller and replugging it, so that Steam no longer picked it up and my Antimicro profile worked correctly, but as of recently, this is no longer possible.
Justification [optional]
Proton is the thing I triggered this bug with, and the one which later fixed it.
Risks [optional]
References [optional]