The TL;DR is that the organization that controls the HDMI standard won’t allow any open source implementation of HDMI 2.1.
So the hardware is fully capable of it, but they’ll get in trouble if them officially implement it.
Instead it’s officially HDMI 2 (which maxes out at 4k @ 60Hz), but through a technique called chroma sub-sampling they’ve been able to raise that up to 4k @ 120Hz.
However there are some minor reductions in picture quality because of this, and the whole thing would be much easier if the HDMI forum would be more consumer friendly.
In the meantime, the Steam Machine also has display port as a completely issue free display option.
Exactly that.
Its mostly common on commercial devices still, but it is defined.
https://www.usb.org/document-library/usb-type-cr-locking-connector-specification
As an example:
https://www.startech.com/en-us/cables/usb31ccslkv1m
Though again, a lot of this could be mitigated with a loop, strain relief, and inserting from above into a port rather than letting gravity pull it down. But it would be nice to see side screw locks be more common with usb-c.
That usb-c connector with side screw locks looks like a future I want to live in.
It’s futuristic, but it’s open and not corporate. It’s miniaturized and sleek, yet still mechanically rugged.