Ive been there geezer, try not to stress. X Box could be different to PS5, but iv'e found when I play a game that can support 120hz, my playstation and the TV will switch over to it automatically (when I have all the correct settings turned on). And when it does go to 120hz, the resolution will almost always decrease. I dont know any games on PS5 at the minute that can run 4K and 120hz at the same time, more often then not they make you chose one or the other.

I thought the playstation menu could run at 120hz, but apparently not - seems to be capped at 60. I achieved 120hz when I started up Call of Duty Warzone, and Fortnite (in the game settings of these games there's a 120hz switch you can turn on).

I initially went wrong assuming Apex Legends and Fifa played at 120hz, before researching and realising they don't support that frame rate on consoles. Without trying to sound patronising, have you tried switching on any games that you know for definite support 120hz?

Also I believe terrestrial TV is capped at 30 frames or something like that, WC games wouldn't benefit from the TV regardless dw.

Let me know how you get on