@IgorI'm not quite sure if this is the problem but the current docker install script which I followed from your link above: https://docs.docker.com/engine/install/debian/#install-using-the-convenience-script
leads to download a script that differs from the script used in procedure install_docker in armbian-config. Thus errors 404 on docker install.
On armbian-config script the expression
echo "deb [arch=$(dpkg --print-architecture)] https://download.docker.com/linux/${family,,} $distribution edge"
returns the broken value of
deb [arch=armhf] https://download.docker.com/linux/ edge
which leads to error when doing apt update for docker.list so unable to install docker-ce
The script from the link I stated above puts this in the docker.list:
deb [arch=armhf] https://download.docker.com/linux/debian buster stable
which seems ok and the install goes further and installs the docker-ce.