Every time you plug an iPhone or iPad into a Mac, macOS can create a full encrypted backup. Over a few device upgrades, those backups quietly consume hundreds of gigabytes.
Short answer: delete old backups from System Settings > General > Storage > iOS Files, or remove them manually from the hidden MobileSync folder.
The native path
- open the Apple menu and click System Settings
- open General, then Storage
- scroll to iOS Files and click the info icon
- review the backups with their sizes and dates
- select old ones and click Delete
On older macOS versions that still use iTunes, the path is iTunes > Preferences > Devices > Delete Backup.
The manual path
If the Storage pane is slow or glitching:
- open Finder
- press Command + Shift + G
- paste
~/Library/Application Support/MobileSync/Backup/and press Enter - each backup appears as a folder with a long random-looking name
- drag the ones you do not need to the Trash and empty it
The folder names map to device identifiers, so check the modified dates in Finder's List view before deleting if you want to be sure which backup is which.
Stopping future buildup
If you mainly back up to iCloud, you can turn off automatic Mac backups when the device is connected and rely on iCloud alone. That prevents the same pile from growing again.
Better next routes
If the weight is not actually backups, continue with How to Find Large Hidden Files on Mac.
For the broader Mac cleanup framing, use What Is Purgeable Storage on Mac?.