I wouldn't advise taking that approach as ST4 folder structure is different to ST3. You can't just copy and paste the folder structure of ST3 into ST4 without then performing additional tasks.
Much better (and supported and recommended method) will be to do a working full backup of ST3 and restore into ST4.
It should not be a problem to work out why your ST3 full backup is not restoring properly as there is usually only a few simple reasons:
- Not enough free space on the device where you are performing ST3 Full Backup resulting in an incomplete/corrupted ST3 Backup file - you need at least the same amount of free space for the backup file, as ST3 currently takes up (e.g. if your ST3 install taked 10GB, you need at least 10GB free space)
- DO NOT backup to a cloud drive/app. Only backup to local storage, or an attached USB drive.
- Ensure your copying of the ST3 Backup file to the ST4 device (if different) isn't corrupting it (avoid using cloud apps)
- When restoring your ST3 backup file into ST4, you need as much free space as the actual ST3 backup file (i.e. if your ST3 Full Backup file is 10GB, you need at least 10GB free space for ST4 to restore that file).
- DO NOT enable iCloud Sync on your ST4 device before you restore the Full Backup. Only enable this after you have successfully restore the backup file into ST4 and verified it is all there.
There usually isn't anything outside of the above that causes the Full Backup from ST3 to not restore into ST4.
I literally copy and paste the above into posts every week and the problem is always in one of those stages.