Downgrade to winbuild 1903 (yeah you have to install your programms again(chocolately is very helpfull fot that)(you can also create a new partition before reinstall windows and save your games there)), it's the only thing that's working for me
Topic on Talk:Forza Horizon 4
There have also been a significant number of issues with nVidia drivers breaking the game. You can verify by reading driver release notes. So nVidia users might need to try different a driver revisions as they will fix an issue in one release then break something else in the next release. The same applies to Forza 7 but issues occur less often.