I also have Win11, on an LG C2 and an Nvidia RTX 3080 (all on latest updates).
I am having the same issue. All the suggested fixes only help temporarily:
The moment my computer goes to sleep, and I wake it back up, Dolby Vision is turned back on (although that is not actually reflected in the UI, where DV still appears as "turned off").
After every wake or boot, I have to go back into the settings. What is strange however, is that simply opening the settings menu restores everything to normal.
It's as if Windows forgets that DV is off, and the moment it actually has to check the settings to show them on screen in menu, it realizes "Oh yeah, DV is actually turned off, sorry about that" and it switches back. It's extremely annoying.
I do not want to permanently turn off features like HDR or hardware-acceleration for my current setup, otherwise, why did I even buy an LG C2 and a 3080? The features or the components are obviously not the issue. This has worked perfectly fine in the past, so no reason to break it now.