By default your backups are located under ~/Library/Application Support/MobileSync/Backup/ on your Mac. While you won't be able to change the default backup location, you can navigate to this folder and move the backup to another folder or external HDD/SS
The default iTunes backup location is set to the PC or Mac's primary disk, and in macOS 10.15, iOS backups as created by Finder are stored in the same place ...
Open the default Backup location in Explorer using the Windows Run command. Press ⊞ Win + R and the Run window should appear. Enter %APPDATA%-Apple Computer- ...