I was having some issues with what was being synced to my desktop app and my android app. I deleted the files at the sync point target (a Nextcloud server). The notes and notebooks on my android device are the correct versions. I tried to sync from my android device but I get a response:
Last error: Fail-safe: Sync was interrupted because 100% of the data is about to be deleted. To override this behavior disable the fail-safe in the sync settings.
I'd like to upload the versions of the notes and notebooks that are on my android device to the sync point, then sync my desktop app to the sync point so everything is up to date across both apps. I've got a backup of my desktop app files but when I try to export the profile on my android device, I get an error Could not export files: Directory could not be created
This was really more of an extra safety net than a requirement, unless you want to wait for a potential fix for the export (or at least an explanation from somebody who knows better than me) then there is nothing stopping you from trying to sync it to a new target, the fail safe should kick in if it goes wrong but I can't be certain. Annoyingly you won't even be able to sync to the local file system as an extra sync target backup in lieu of the other options due to the aforementioned issue.
Other than that you are looking at ADB stuff to get your profile out I think.
Basically, unless anybody else can think of any alternatives, I think your only option is to bite the bullet and just go ahead with trying to sync to a new (as in completely new, never sync'd) target.
I went ahead and created a new folder in Nextcloud. If the original sync point was /path/to/nextcloud/joplin then the new one is /path/to/nextcloud/tmp_joplin.
I changed the sync path on my android joplin app and tried to sync to that new location but got the same error:
Last error: Fail-safe: Sync was interrupted because 100% of the data is about to be deleted. To override this behavior disable the fail-safe in the sync settings.
This is why I suggested a totally different target like dropbox, the link I posted on GitHub (FAQ | Joplin) exists because of this exact issue, you can't use a different target within the same sync target type or it will still try to delete your data and activate the failsafe (I'm not sure of the technical reason behind this as a concept but it is documented and is simply how it behaves)
I want to provide an update just in case others come across this issue.
I ended up not implementing the steps outlined above. After reviewing the changes in the notes that were affected, it was pretty minimal. I transfered the changes to a text file and emailed it to myself. I then imported a recent jax file I created before troubleshooting this issue, then implemented the changes from the file I emailed to myself.