There is an extreme mismatch between official u-boot build documentation and the binary files provided.
The mainline u-boot repository doesn't offer Amlogic defconfigs, and instead instructs you to use some quirky old 2017 amlogic branch that just spits strange compile errors, which on top of all requires you to use additional Amlogic tools to sign the files, making it very complicated and mysterious to build a functional u-boot by yourself.
However the binary files in this repo seem to be mainline and working.
However they seem to be also non-standard , i.e. not offering lzo kernel image compression support (LibreELEC kernel fails with "unimplemented compression type 4").
It would be great if we just had working u-boot images for everyone, not just Armbian, and even better if we could compile them ourself with up-to-date instructions.