- Yes, it can work 100% offline (locally)
- There's a sync to any webdav for data and number of clouds including self hosted nextcloud. You can even go with joplin server (beta) and keep everything in a separate (local or remote) database.
Although, there are only options to sync from every 5 min to 24 hrs, there's an amazing plugin for backup that can save any increment of data (including visual settings of the app, I heard) with any time period in hours (say once a week). Also you can adjust how many copies of data it needs to hold.
It can even save backup on network drive (say samba).
And all that is from GUI, no scripting required (although if you're in linux, you might need to know how to mount network drive if you wish to use it)
Link to backup plugin