For those who were in the conversation earlier it is now confirmed that those TVs with the 40gbps HDMI 2.1 connections will NOT be able to push 4k, 120hz at 10bit 4:4:4 with HDMI enabled.
Sony’s latest the 8k Z8H has this problem and the option is clear, you can choose between 4k 120hz or 4k 60hz with 10bit, HDR and 4:4:4 subsampling.
So far the only TVs I’m aware that are affected are the 2020 LG CX and Sony Z8H.
In order to get the full next gen experience you need to ensure your TV or monitor has a full 48gbps bandwidth HDMI 2.1 port.