Same issue, game crashes on launch. Steam version of the game, Avast on Windows.
I tried a million things, including turning off all Avast shields, and core shields, and adding scan exceptions to steam/x86 and the forza folder, and it would still crash. I then fully uninstalled Avast, and restarted, and the crashing problem went away.
This is pretty ridiculous, the whole point of settings exceptions, is to stop avast from breaking things in that directory. Whats the point if the exceptions you set dont work?