For instance if you tool the shark fin on the back of an lmp car and kicked the back side out left or right and have the amount based on steering input. Any reason this wouldn't work or isnt used?
I can think of a couple reasons this might not work so well:
1) anything you do with a little rudder is going to work the air, strip some energy away from it and also introduce turbulence, which will make the rear wing less effective.
2)controls: steer left, rudder goes trailing edge left: This makes a force that pushes the back of the car to the right... You're trying to turn left, this force is fighting you and reducing the overall force you can produce to the left, the way you want to go.
OK, so set it up the other way; steer left, rudder goes trailing edge right: This is probably good actually. It produces a slight increase in the force the rear end of the car can produce in towards the center of the turning circle. It's not until you are counter steering in a slide, where the rudder is again pointing the wrong direction, reducing the effectiveness of the weathervane effect the big fin provides.
3) the effectiveness of such a tiny wing mounted so far aft in dirty air is likely to be very low.
https://www.youtube.com/watch?v=eKr9VlaBGTw
IMO that supercar tilting wing looks slow to react and super lame.
It's pretty easy to generate force with wings... how about a wing mounted vertically @ the longitudinal CG of the car with a simple controlled trailing edge flap. It produces lift inward toward the center of the turning circle and a rolling moment that combats the load transfer to the outside tires.
then there's this. A solidly mounted billboard does make sideforce when you get the car in a corner with slip angle. Or a crosswind XD
https://www.youtube.com/watch?v=y0l3JP_wkvk&t=814s
Are these vertical wings safe when you spin the car at high speeds? Almost certainly not.