Here is the only method that works for me on win 11:

go to local file folder of the game: right click Forza Horizon 4 > manage > browse local files

search for the file TargetHardwareProfiler.dll > delete this file

The game should start now.

When you start the game for the first time, you have to log in with your account data. A login window will pop up. If the login form does not appear after a short time, close the pop-up and press "x". That's how it worked for me.