It cannot do 4K 120 Hz on any Mac and is limited to 4K 60 Hz. See this thread: https://forums.macrumors.com/threads/mac-mini-4k-120hz.2267035/Anyone using the new LG C2 with an M1 Max?
It seems to be largely a MacOS issue. I would not recommend using the LG OLED TVs with Macs for anything but movie watching at this point.