I can get 8k@30hz at 4:2:0 but cannot get 4k@120hz at 4:2:0 on Q800T

[RouDeR]

My GPU is GTX1080ti (tried with latest and older drivers)
Windows 10 build 1909.
Tried with several High speed HDMI cables from 18gbps to HDMI 2.1 with 48gbps

With Input Signal Plus enabled on HDMI port 4 the available PC resolutions are:

1440p - 60/120hz 
4k (2160p) - not at all
8k - 30hz 

The PC and TV have no problems run at 8k @30hz in 4:2:0  but  when I try custom resolution for 3840x2160@120hz or even 61 hz - the picture just dissapears, basically  I can't achieve anything above 60hz If I run above 1440p which is noncense because the 18gbps are enough for 4k@120hz 4:2:0,>
Also I can drive the TV at 4k@60hz 4:4:4 so the only logical explanation is that Samsung is intentionally or accidentally  crippling the TV which is  mindblowing.

There are many people that are using their 2019 Q90R  as PC  Monitors with 4k@120hz 4:2:0 and here I`m with a 2020 8k TV that can't do It, because of unknown reason ?

I`m with latest 1115.5 update

[RouDeR · Accepted solution]

OK this seemed to be issue with Windows registry (at least in 1909 build) I managed to fix it with program called CRU which enabled 4:2:0 for all resolutions by default. I`m perfectly able to do 4k@120hz 4:2:0 with mid-range level HDMI cables.