Local storage is the name given to what is essentially the master version of the data Jupiter manages - all the inbox tasks, the big plans, the recurring tasks, the smart lists, metrics, stats about them, links to Notion etc.
It is managed by the Jupiter CLI.
Right now, it's nothing more than a bunch of files in a directory. The tutorial handles setting it up,
but it's essentially a
jupiter init inside that directory.
At this point Jupiter does not do any special backup or replication of this data. It's up to you to do so. Git with GitHub/GitLab is a good solution to use here. But you can just as easily use Dropbox/Google Drive/Apple Cloud or any other file sharing solution. You won't have an easy restore option in case of mistakes though.