Hello @Mullato, the steam-devices package should provide the udev rules needed to use the Switch Pro controller with Steam, however, the version in Debian Stretch's repos is too old and does not include the Switch Pro. The closest package to your system that has that controller is steam-devices from Buster. You should consider slamming that in to place or extend the current udev rule set to include the relevant entries. (Which you've already noted.)
Thank you so much! This worked like a charm. You have no idea how much I appreciate the rapid response @kisak-valve
Nothing extracted yet.
Please describe your issue in as much detail as possible:
After connecting the switch pro controller either via USB or via bluetooth, this same issue will occur. The controller will work perfectly fine in big picture mode, however no buttons will function properly on the controller other than the screenshot button once any tested game is loaded. (I have been testing this on Stardew Valley and Enter the Gungeon with various controller configs) Notably, though, if you hold the home button, the joystick will work as intended. I have already updated udev rules.
Steps for reproducing this issue: