CaWeissWz

Unfortunately I was not able to work on this topic appropriately and thus could not provide any helpful information.
But in the meantime, others have done a lot of work on this topic. Thank you @uablrek for the link.
So I tried and built a new image (from main branch) after https://github.com/armbian/build/pull/8449 had been merged. I can confirm that the Rock 4SE now boots with this version.
 
Thanks to everyone involved for the solution!

Unfortunately I was not able to work on this topic appropriately and thus could not provide any helpful information.
But in the meantime, others have done a lot of work on this topic. Thank you @uablrek for the link.
So I tried and built a new image (from main branch) after https://github.com/armbian/build/pull/8449 had been merged. I can confirm that the Rock 4SE now boots with this version.
 
Thanks to everyone involved for the solution!

Yes, I know how to compile images. I'm still learning how to use git efficiently, though. 
Git bisect, I had never heard of before; but from what I read, is seems to be the right tool to find the breaking commit. But before I start into this possibly lengthy process, I came up with one theory, that I intend to check first:
 
The initial assumption was, that the error is due to an API incompatibility in the Arm Trusted Firmware. My first intention was, to check if a newer version of the ATF was available, I just didn't know for wich part exactly I should look.
Now I found out, that the working Image starts the "BL31"-thing right at the point where the current images fail:
 
So, the first thing for me to check will be which version of "BL31" is used for the current images and if a newer version would be available and could be used instead.
Unfortunately, i might not be able to work on this until next week. But I will report back as soon as there is new information.,