I just wanna play Tony Hawk with a GC controller man
First of all.... Gamecube controller? Gross.
I kid... kind of...
I am not a fan of whatever the hell steam does with controllers. Have you tried using something like this?
https://www.x360ce.com/GC controller is the best controller, facts don't care about your feelings. And there's whole labyrinth of drivers and procedures you're supposed to follow to set it all up and when I do it all doesn't work anyway. I indeed used that program and it recognizes the GC controller but it still won't work in Steam games for whatever reason.
Did you try disabling the steam configuration like this?
https://support.rocketleague.com/hc/en-us/articles/360022354994-How-do-I-Disable-Steam-Controller-Configuration-
Ok it actually works now, but somehow the inputs in game don't match with the x360ce settings so I'll try to figure that out. Thank you very much.