Hello BayaDM and welcome to the Microsoft Community!
Based on your feedback, you are experiencing issues with Dolby Vision and HDR10+ not being available when displaying HDR content!
Even though you are using an hdmi 2.1 cable, the transmission bandwidth is not enough!
You can try replacing the DP cable to see if that solves the problem.
Because I had a similar experience myself
When using hdmi to connect to the computer, it caused the monitor screen to be corrupted and the frame rate could not be improved.
Replacing the dp cable solved the problem for me.
If you have a dp cable you can try it.
I hope you find the above information helpful.
Kirito|Microsoft Community Support Specialist