One of the limitations of the AMDGPU Linux kernel graphics driver has been the lack of its support for HDMI 2.1 and later. AMD has wanted to support HDMI 2.1+ functionality under Linux but it's been legally blocked by the HDMI Forum. But anxious independent users have been working on open-source patches for wiring up HDMI 2.1 into the AMDGPU driver outside of the realm of AMD and the HDMI Forum's blessings...