You haven’t provided any details on the type of NAS, but is it by any chance https://forum.syncthing.net/t/synocommunity-syncthing-package-update-1-19-0-24-for-synology? If yes, then you should be able to find some instructions and tips on what to do next in that topic.
For the record, the config wipe issue reported there was caused by a faulty installer specific to the NAS. It’s not something that was done by Syncthing itself.
As for the backup restoration, what I personally always like to do is to set all folders to receive only first, then wait for the synchronisation to finish, then reset “local additions” and restore their original folder type. This way you can re-use the database too, so there’s no need to re-index everything from scratch.