I created a GitHub “gist” that people might find useful for local Nextcloud Maps development. It is a work in progress, but in the current state it works for me. Summary from the Readme:
Develop Nextcloud Maps locally using Docker, with a custom git-based snapshot system for easily saving and restoring the complete state of the local Nextcloud server instance.
Assuming you have Docker installed on your local machine, you should be able to git clone the gist to ~/maps, run ~/maps/init.sh, and (after a few minutes) login to a fresh local Nextcloud server with Maps already installed at http://localhost:8000 (login admin:password).
I’m curious to know if it works for other aspiring developers.