Steam currently doesn't support the official Nintendo GameCube USB Adapters: the controllers do not appear, and their inputs do nothing, both in Steam and during games. Enabling Steam Input for generic controllers does nothing.

SDL does support these controllers, but for it to be able to use them:

• SDL must be compiled with the libusb dependency (all the libSDL3.so.0 bundled in Steam aren't)
• The following udev rule must be installed:

SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", ATTRS{idVendor}=="057e", ATTRS{idProduct}=="0337", TAG+="uaccess"