I have the same tv and question.
Im able to get my tv to work on 4k120 and 8k30 via hdmi 2.1 cable and my computer.
but less than a day of use and my one connect box keeps giving me a one connect cable is unhooked error. and the one connect box is real real hot.
I switched it back to 4k60 and havent had any issues.
So is the tv updated to hdmi 2.1? what do i need to do to either update it or confirm its updated?