you said Gamecube controller with a "USB end".... so I assumed a third party gamecube controller, aka not an original GC... but a usb controller meant for pc use (those exists), because original gamecube controllers... dont have a USB end.
And reguardless most games dont have GC support bc its not common to use them outside fighting games, if you want to, just find a software that translates to xbox imput, theres plenty out there and my point was that you should already expect 99% of games to not have support for it anyway.