In order to delete old backups from your Mac, you will need to delete the backups manually from the file they're saved to.
The directory for that is either ~/Library/Application Support/MobileSync/Backup or ~/Library/Application Support/iMazing/Backups which you can find with the Finder app.
- Upon opening Finder, go to "Go" in the toolbar at the top of the screen and click on "Go To Folder".
2. Copy and paste the file directory and it will show all of your backups. We also recommend to right click or use two fingers to click if you're using a Macbook to bring open an options menu for each backup file and click "Get Info" to see the timestaps of each file to make sure you don't delete the wrong one. )
From the Backup folder, you can delete all of the backups that are shown there which will clear your hard drive of the memory of those old backups.