In case anyone stumbles upon this and, like me, is trying to install docker-compose on Debian Buster-based Armbian (arm64 architecture) the answer, as it turns out, is quite simple...
Install Docker using softy. (Softy does all the work - it's great!) I recommend testing the install with
docker run hello-world
Once that's done and successful, you can just run
sudo apt install docker-compose
and it just works. If you want to test it, paste this into docker-compose.yml:
version: '3'
services:
web:
image: nginx:latest
ports:
- "8080:80"
links:
- php
php:
image: php:7-fpm
then run
docker-compose up -d && docker ps