HDMI not functional

I’ve got a rock 4 SE that is part of the “newer chip set” originally radxa didn’t want to acknowledge they had changed anything but they had.

Long story short they’ve sent me a new ubuntu image. Ubuntu 20.04.6 LTS (FOCAL FOSSA). This image doesn’t seem to be displaying anything on my HDMI at all. Not even the serial output. How can i get my serial output to be displayed on my HDMI port?

I’ve checked my /boot/config-5.10.110-28-rockchip file and all the HDMI stuff is enabled there.

Start checking with different HDMI cable as well as monitor, as far as I remember there are some incompatible resolutions as well as cables (and that happens always, I need two different cables for two computers for my DLP projector, both work great but only on one, particular computer).
Then try other images. If You have old and new board try same set on two boards.
Also - I noticed that one particular version of bootloader boots very very slow, about 1 min, try to wait. Boot without cable connected and then connect it. Is device present on network?

Please note that the 5.10.110 kernel is somewhat “old”. HDMI does not work in all combinations. Especially, the DVI over HDMI mode is broken. So, If you use a HDMI->DVI adapter, output is black.
5.10.160 is the first vendor kernel that supports DVI-over-HDMI.