It's almost November 2020, and I've been pulling my hair out over this as well. I've spent hours searching for answers and in the process of trying suggested workarounds, I've actually broken other games. Very frustrating. Thankfully I've been able to resolve those other issues, but the Dolby Vision black screen remains.
I can at least get NFS Heat to run without triggering Dolby Vision by turning Deep Color mode off in my TV settings (LG C8). But as soon as I try and switch it back on, even after exiting the game, it triggers Dolby Vision and I'm stuck with a black screen.
After several reboots of both the PC and the TV, I'm not exactly sure what I did but somehow things are back to normal. If this is what I have to go through every time I want to play this game, then that's ridiculous. I wish I could get a refund but I'm past the date.