I was referring to syncing to the cloud, re dropbox and onedrive. In that case, there are local folders which are automatically replicated - mirrored, to be exact - on the remote server. I have a lot of onedrive space, but there's no good way to sync linux to onedrive (there is one utility, but I haven't tested it yet, and not sure I want to do it anyway). Dropbox, free, is much smaller, but works great.
There are local syncing tools that are excellent as well. In Windows, SyncBack Free easily takes the prize. You can sync in both directions, one direction, and more.
That FB problem seems to be a FB "feature". I would be very careful what it's syncing. Knowing $uckerberg, you might be publishing stuff either to your timeline or at least to his prying eyes. Check browser extensions, apps and plugins. Check your FB settings. Check startup progs in Task Manager, though Win8-10 don't show 10% of them to the user. I don't use FB because it's a privacy trap.
Unable to save the file? Try in another location, say Desktop. Or a different text editor. Might be a permissions thing. Yes to CherryTree. Simple, but gets the job done.