The HDMI Forum rejected AMD's open source HDMI 2.1 implementation
If you were hoping at some point to see HDMI 2.1+ on Linux with AMD + Mesa, you're out of luck right now as it's simply not going to be happening.
Are there any DisplayPort to HDMI adapters that support hdmi 2.1 and freesync / vrr? I found one on Amazon that is reported to do the former but I didn’t find one that does both.