markrudling What is the result is you execute cat /sys/class/amhdmitx/amhdmitx0/disp_cap over SSH?
480p60hz*
720p60hz
1080p60hz
EDIT: Ok so a bit more experimenting gives me the following results.
Plug into HDMI3 and reboot box. 4k
Plug into HDMI1 4k remains. Reboot box and resets back to 720, with 1080 as other option
Plug into HDMI3 still no 4k option. Reboot box while still in HDMI3 and I get 4k again and refresh rate adjusts per video.
I will do some more research into my tv and if there are differences with the inputs. I know HDMI3 does not have seem to support HDR, perhaps there is something in the auto detect/initialization there? I know HDMI1 supports 4k, but after reboot it defaults, so it must be in the initialization.
Thanks for trying to help, will be very glad if we can resolve this.
Results when 4k enabled on HDMI3
480i60hz
480p60hz
576i50hz
576p50hz
720p60hz
1080i60hz
1080p60hz
720p50hz
1080i50hz
1080p30hz
1080p50hz
1080p25hz
1080p24hz
2160p30hz
2160p25hz
2160p24hz
smpte24hz
smpte25hz
smpte30hz
smpte50hz
smpte60hz
smpte50hz420
smpte60hz420
2160p50hz
2160p60hz
2160p50hz420
2160p60hz420