Hello @cpf, this issue is outside the scope of Steam in general and needs to be resolved at a system config or distro level for the affected devices.
That said, you should be able to adapt https://github.com/denilsonsa/udev-joystick-blacklist to your needs.
Closing as out-of-scope.
Nothing extracted yet.
Your system information
Please describe your issue in as much detail as possible:
I would expect my keyboard to not be recognized as a controller. This causes issues in a couple of games, like csgo (Where -nojoy luckily fixes it)
When running a proton game though, it completely messes with everything, and causes the game to misinterpret everything. e.g. Monster Hunter World thinks the controller is always moving top-left.
I have an ergodox infinity, which might be the reason why.
I have found no way of turning off controller support, or making it clear to steam that the keyboard shouldn't be recognized as a controller.