Both posts you linked are 5y old, at that time backup tools were actually still in the supported category on the Process for reviewing classic confinement snaps page… very shortly after these posts the system-backup interface has been created and in turn this set of applications has been removed from the supported list, since the functionality is now covered by that interface…
While i indeed doubt that system-backup would help your specific case at all, these posts are not really relevant anymore… (and pointing to other old posts will likely not help either, the list on the process page is the mandatory source for granting/denying classic)