The HDMI Forum, responsible for the HDMI specification, continues to stonewall open source. Valve’s Steam Machine theoretically supports HDMI 2.1, but the mini-PC is software-limited to HDMI 2.0. As a result, more than 60 frames per second at 4K resolution are only possible with limitations.
It might be possible to get into output wirelessly, it has a dedicated radio for video output so presumably if you just stuck an adaptor into your TV you could just cast to it. Could be quite a nice setup if you wanted it to be able to connect to both your computer in the study and your TV in the living room.