No worries it is sometimes hard to get your point across online .
The issue could then be an issue with the nvidia + windows hdr + the screen.
Have you tried tomb raider on your TV also? Because HDR does not necessarily means more vibrant and saturated colors it means that the screen can display en extended range of color. more color at the same time and have improved contrast. And it all depends on the game hdr implementation as well.
For exemple in tomb raider for exemple I find that the green of the leaves is way more saturated in sdr than in hdr. In hdr the leaves have more what I would call real like color (sorry it is hard to find the words to explains). But if you look at a fire for exemple the sdr version doesn't pop out and looked more of a blob when the hdr version you can see all of the gradient from the heart in yellow to the exterior flames in bright red.
I really want to emphasize that HDR doesn't not mean necessarily an explosion of color like you see on samsung phone screens even if that's what we expect from all of the advertising . For exemple the latest ratchet and clank on PS4 can look weird in HDR as you would expect just saturated colors everywhere, the game still have them but it is more subtle in its presentation.
Yes, as you wrote, that doesn´t mean, that all colors on the whole Screen should be very vivid, or vibrant, but the color reproduction in those games is like through some grey filter. As you said, I saw this kind of behaviour in Tomb raider too, but yes, when you look into fire, it Looks nice (like in Battlefield V). The bright parts of the Screen, where Peak brightness is in game look good, but on the rest are the colors just faded. F.e. in Resident Evil 2, the main character has on his Body this bulletproof vest. This vest is in SDR much more black and in HDR is like through Grey filter (you can see this behaviour on the other colors too). In Forza Horizon too, the cars look good, but when you come to some yellow field, this color is much darkder as in SDR, in SDR is the yellow really juicy, vivid. I feel, that the saturation has to be improved in HDR Content, cause in SDR it has for me better contrast Ratio even though the whole Screen is brighter in all areas.
It is possible, that these verstical dimming zones are the reason of it and it is not capable to make the picture right, I don´t know. When it is so, why look the youtuve Videos OK? Without any Grey filter, or so? Or other games like AC Odyssey? It is propably more complicated as we think, but I think, that we need some Firmware update here, some tweak inside the monitor for HDR.