In my opinion and experience, armbian-config is a horrible pile of hacks that are almost guaranteed to eventually eat your data. As such, in my opinion the only sane action is to stay far clear of it.

@Hqnicolas how to build the current u-boot RK356x ?

In the meantime I got HDMI also working through my AVR. I just changed the cable and that did the trick... One thing to mention: the system seems to be allergic to hot-plugging the HDMI cable. So if I connect/reconnect the cable during runtime, the HDMI output will be gone. It requires a reboot WITH CABLE CONNECTED. Not a big issue from my pov, but important to know...

Please prepend the commands with LC_ALL=C like "LC_ALL=C apt update" and post the output again.

ping @metalhard