I was being a bit cruel. It's an HDMI 2.0 port, which is useful for presentations (a USB-C to HDMI dongle lives in my backpack for that reason). 2.0 will drive a 4K monitor at 60 fps. Never tried that, but, IIRC, the original USB-C port (and HDMI 2.1) could do it at 120 fps (which, for my terminals, would be... totally overkill, just like 60 fps already is).
While I agree HDMI 2.0 on a new for 2021 machine is an odd choice, displays can still be connected to the Thunderbolt 4 ports much like the previous gen. Apple's spec sheet says two external monitors at 6k/60hz supported this way via TB4.
All of this is to point out, has anyone confirmed 4k/120 on the thunderbolt port? Given the 2x6k monitor output 4k @ 120hz sounds like it should be possible, unless Apple have nerfed the output.
