The only optimisations that only Geforce Experience can do is changing the graphics settings for the games. At least that’s the only optimisations I know of from Geforce Experience.

This doesn’t really have much to do with Forza Horizon 4. As, if it’s like Forza Horizon 3, you will still be able to play the game online and offline. This is what the stop killing games wants the other publishers to do.