@anirban-dutta I use command like this npm install git+https://github.com/me-cooper/nodebb-plugin-makesmart-gallery.git when repo is not recognized by npm install
Just remember to add .git at the end of github repo url.
Is there some way to save and load the settings of a plugin (or the whole nodeBB) to/from a config file instead of mongoDB ?
No built in way, but there is nothing preventing you from writing your plugin to use a config file instead of settings stored in the database.
When your nodebb starts instead of loading your plugin settings from the database you would read it from the file.