Sorry, it's the Steam version.AC will work in pro mode no problem, same as G923 mode - just reassign the controls in the options of the game.
Forza can be tricky, especially if this is FH4 and doubly so if it’s the Steam version (you didn’t confirm). So which version of Forza is it and which store version?
Also, anyone able to share settings for AC? Not sure I have the wheel set up correctly, getting a lot of oscillation when driving in a straight line at speed.