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.
Yes, DP converts to HDMI natively. But because HDMI has so much proprietary BS built in, going from HDMI to DP requires an active adapter which strips out the proprietary BS.