It's definitely much easier to do that on docker than with apt packages, and docker was designed for thst. Just do a save/load, https://docs.docker.com/reference/cli/docker/image/save/ and like I mentioned before this is much more stable than saving some .deb files which will break the moment one of the dependencies gets updated.
Most people will use whatever docker compose file a project shows as default, if the project hosts the images on dockerhub that's their choice. Plus I don't understand what's the problem, GitHub is also proprietary and no one cares that a project is hosted there.