Nice writeup! Another unfortunate side effect of using symlinks is that Hyper Backup will display a "partial success" error after backup if you select the mounted folders. Confusingly, it will display the folders when you create the job but won't backup the files. The good news is that backing up the Synology Photos application will not display the "partial success" error, but note that it won't backup the original files. You'll need to select the source folders.