Im having the same issue as everyone else. Set the game to HDR and exit out and try to restart the game and it will initially crash silently the first time, and if you try to start again it will finally start up, but HDR mode is disabled again. It also seems that only HDR10 is available for me too, using a LG CX, Win 11, TV is set to PC/Game mode.
Also seems like even if you enable HDR in HDR10 mode and try to play the game, it appears the menu and UI is in 4K HDR, but when you go to actually race, its like its in 1024X768 SDR. I have everything maxed out for graphics at 4K with DLSS DLAA turned on, system specs are below.
I9 14900KS
64GB DDR5 7200mhz
4TB Samsung 990 Pro SSD *game is installed here*
2TB Samsung 980 Pro SSD *operating system is here*
ASUS TUF z790 WIFI PLUS Motherboard
ASUS TUF 4090 OC GPU - Latest NVidia Drivers Installed
1000W ASUS TUF PSU
LG CX TV, Calibrated HDR under Win11 using HDR calibration tool to 800 nits *peak brightness of TV*.
*Side note: Ive tried SDR, HDR via Dynamic Tone Mapping and HGiG and even all tone mapping turned off, and SDR displays correctly at 4K, whereas HDR when enabled is displaying at 1024X768 S DR. It also switches from RGB 10bit 4L10 to YCBCR444 8bit 4L10 for some reason too. I tried going into NVidia Control Panel and setting display to YCBCR444 8 bit to match what the game is trying to display at, but it still reverts back to 1080X768 and turns HDR off when you actually start driving. The menus and UI still remains in 4K HDR though. Did not have any issues with same hardware and settings on F122 or F123.