https://wccftech.com/forza-horizon-3-xb1x-hdr-dark/

Following yesterday’s Forza Horizon 3 XB1X patch, various users have reported that the game’s is now too dark with HDR enabled.

Microsoft and Playground Games released the highly-anticipated 4K update for Forza Horizon 3 yesterday, but if multiple users on Reddit are to be believed, the patch makes the game way too dark on some occasions.