Kodi Community Forum

For three years there has been a bug report around 4K@120Hz being unavailable via HDMI 2.1 on the AMD Linux driver. Similarly, there have been bug reports like 5K @ 240Hz not possible either with the AMD graphics driver on Linux. AMD as well as the X.Org Foundation engineers have spent months and had code working internally and then the past few months were waiting on approval from the HDMI Forum. Sadly, the HDMI Forum has turned down AMD's request for open-source driver support.

On what basis? From what you write I gather that Intel and Nvidia don't share the problem, correct? Nvidia has closed source drivers IIRC, is that the case for Intel too? Is that how they manage to get support?

Intel works around this by having a DisplayPort 2.0 to HDMI 2.1 protocol converter (PCON) on some of their cards. That way their open source driver doesn't have implement HDMI 2.1.