I definitely understand the lack of polish for such a new board, I already very grateful for where I got so far. As for latest being broken, I mainly wanted to make sure others looking could find the 20.11.5 build which boots fine,.
I managed to get networkd and timesyncd working, and found a way to get the gmac interface name stabilized using a systemd .link file targeting the device Path. Wondering if a udev method would be preferred? In this case I believe targeting by driver will not work, for some reason it seemed to be missing when I tried.
I was looking into rebuilding an image with these tweaks included, and so I could maybe contribute some of it back, but this is where I started struggling. The build environment is very picky, and while I have a few x64 linux systems around, none of them were full Ubuntu or capable: Synology NAS with docker (lacking bin fmt tools), Chromebook with linux crostini VM and docker (lacking loopback devices). Now that I finally got a build environment running, I'll try to see where I can help.
Thanks for the pointers on the existing board customization. If you have any suggestions on how to improve the handling of multi adaptor boards in the scripts, I'll try to see what I can do.