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.
Likely moreso that they’re facing pressure from other competitors in the industry that see Steam and open source in general as a threat to their business model. The HDMI forum is made up of industry leaders, and naturally Microsoft and Sony are there.
https://hdmiforum.org/members/