Came across this forum looking for help, since I've been having the same issue with an Xbox controller.

It only works in the main menu, and only to select a game mode with the D-pad and confirm with A. As soon as you get to the car select screen, no buttons work anymore, and they continue not working during actual racing.

I was able to use an original xbox 360 controller successfully in both 3.8 and 4.0.  In 3.8 it looked like the game resolution was much lower than my 4K monitor.  In 4.0 the resolution was perfect.  Can you get on nVidia games list so I can add filters using the new nVidia app (alt-z)?