Thank you SteelMan for the pointer.
Downloaded the rolling build and wrote it to my USB using balenaEtcher in Windows, the resulting USB was MBR and I could read the boot partitions contents. That's a massive improvement from using the images from https://www.armbian.com/uefi-arm64/ which were GPT and regardless of writing the USB under Windows/Linux the boot partition was unreadable.
My box is probably an A95X Max (S905x2 SOC, 4G Ram, gbit ethernet & 5g wifi) so the uboot should be u-boot-s905x2-s922
All that's left is to find the best dtb
Thanks for all the help