I can't take credit for the systemd unit files, I found those examples ages ago. I've updated them to use the newer Docker Compose plugin.
Each file has its folder locations in a comment at the top. Place the various files in their locations, and then:
systemctl daemon-reload
systemctl enable docker-compose@swag
systemctl enable docker-compose@mediaserver
systemctl enable docker-compose@nextcloud
systemctl enable docker-compose-reload.timer