I have found the Armbian sources to be a valuable source of information.
It has been several years since I tried, but it used to be necessary to build the Armbian linux kernel using a Debian system. I run Fedora, so what I had to do (back in 2017 or so) was to use VirtualBox to set up and run a Debian system, then use that to build Armbian. This was a big pain in the ass, to say the least. The main benefit was that when I pulled the source tree back to my Fedora system, I had object files as (bread crumb) markers to help me identify exactly which source files were used in the build.
The current instructions describe using Docker to build Armbian on Fedora. Unfortunately Fedora 32 has completely broken Docker and various suggested workarounds fail completely.
My section on "Exploring Armbian" is turning into a linux kernel tour.
Tom's electronics pages / [email protected]