shadow9d9
For #7, "Section 3, override to NVIDIA color settings and choose 32-bit, 10 bpc, RGB, FULL. and apply"

What is the purpose of this?

The earliest drivers from Nvidia defaulted to 8bpc & Limited range, so you would not be getting the full HDR color capabilities of the 3000 series card and TV/monitor via HDMI 2.1.  if the default has it gray'd out and it's the same 4 settings, then you are OK - You don't have to override, but early on it was not correctly identifying the TV's full capabilities. 
 
essentially, this LIMITED vs FULL option lets you go FULL deep black levels, where limited stops going darker before the TV's capability. it gets technical but you can quickly google if you want to know the finer details of it.  but basically - if card & monitor can support, you want FULL.
 
And the 8bpc vs 10bpc has to do with gradients of color and total color pallette - 8-bit file works with RGB using 256 levels per channel, while 10-bit jumps up to 1,024 levels per channel. This means a 10-bit image can display up to 1.07 billion colors, while an 8-bit photo can only display 16.7 million.  so essentially 5x more colors are possible just by simply changing this setting.. in real-world, things will have better gradients and look smoother.
 
 

Belkin HDMI ultra high speed working cx 65" rtx 3090

nickvdm
Belkin HDMI ultra high speed working cx 65" rtx 3090

Got a link?
 

Cables both the same. ONLY difference is one is braided.

Nickvdm - it would help a lit to have a link or a model number, I find a lot of different belkin HDMI ultra cables. and all the ones I see do not support 4K @ 120hz 48gbps... so that's good if it does or if you know specifically which one works for you.

I posted links. Not sure why they don't show.
 

AV10176bt1M-BLK
AV10175bt2M-BLK

Great, thanks - I updated the main post to include those.

It's been a couple days for me since posting last. Figured I'd share some more experiences. I don't know why, but the black flickering associated with instant game response is completely gone now. The first time I disabled Instant Game Response, the flickering went away. But then apparently I lost my gsync capability. So then I tried the recommended approach of turning it off then on again right before launching the game. It worked! But then I left it on and have played a number of different games over the past couple days without issues with the TV even after involuntary reboots (I double checked... it's definitely on in the settings, and I see the popup when I launch a game)
 
But I am experiencing instability with my PC. I have 9900k with the 3090 (MSI Ventus) and it's powered by a HX850i and have two monitors the CX and a 32" Samsung 4K. But with spontaneous reboots while gaming, it really smelled like a PSU issue. But 850W is definitely fine, especially with the very efficient Corsair HX. I never bothered hooking up the diagnostic cable (mini USB into USB header) and then I can monitor everything about voltages (in/out), peaks, temps, fan speeds etc. I can say that during benchmark tests and throwing the kitchen sink at it, the PSU barely broke a sweat. The biggest peak I saw was in the 560W range. So the PSU is fine. Don't let people convince you to buy a 1000W+ PSU to power the 3090 beast. 
 
What I actually think is happening is the card is overheating and forcing a reboot. While monitoring temps, I'm definitely seeing results in the high 70s... and it looks like it might trip at 83C (according to Afterburner settings -- stock values). I'm watching this closely because normally when I'm actually playing a game, I'm not really watching for temps -- and when it trips, it's too late. But it happened twice last night. It seems to happen after playing for about an hour or so... it seems the card needs time to heat up gradually.

So that's my next struggle. I haven't played around with underclocking it yet -- I feel like I shouldn't need to especially for this price. I have the latest drivers as of 3 days ago. No Man Sky seems pretty fragile with stability compared to Assassin's Creed Odyssey -- both 4K Ultra, definitely getting ~90FPS in both games which is a joy, but both games have rebooted my PC.

morness
It's been a couple days for me since posting last. Figured I'd share some more experiences. I don't know why, but the black flickering associated with instant game response is completely gone now. The first time I disabled Instant Game Response, the flickering went away. But then apparently I lost my gsync capability. So then I tried the recommended approach of turning it off then on again right before launching the game. It worked! But then I left it on and have played a number of different games over the past couple days without issues with the TV even after involuntary reboots (I double checked... it's definitely on in the settings, and I see the popup when I launch a game)
 
But I am experiencing instability with my PC. I have 9900k with the 3090 (MSI Ventus) and it's powered by a HX850i and have two monitors the CX and a 32" Samsung 4K. But with spontaneous reboots while gaming, it really smelled like a PSU issue. But 850W is definitely fine, especially with the very efficient Corsair HX. I never bothered hooking up the diagnostic cable (mini USB into USB header) and then I can monitor everything about voltages (in/out), peaks, temps, fan speeds etc. I can say that during benchmark tests and throwing the kitchen sink at it, the PSU barely broke a sweat. The biggest peak I saw was in the 560W range. So the PSU is fine. Don't let people convince you to buy a 1000W+ PSU to power the 3090 beast. 
 
What I actually think is happening is the card is overheating and forcing a reboot. While monitoring temps, I'm definitely seeing results in the high 70s... and it looks like it might trip at 83C (according to Afterburner settings -- stock values). I'm watching this closely because normally when I'm actually playing a game, I'm not really watching for temps -- and when it trips, it's too late. But it happened twice last night. It seems to happen after playing for about an hour or so... it seems the card needs time to heat up gradually.

So that's my next struggle. I haven't played around with underclocking it yet -- I feel like I shouldn't need to especially for this price. I have the latest drivers as of 3 days ago. No Man Sky seems pretty fragile with stability compared to Assassin's Creed Odyssey -- both 4K Ultra, definitely getting ~90FPS in both games which is a joy, but both games have rebooted my PC.

Sounds more like a power supply issue.