- Make sure your iPhone is connected to your Mac.
- Open Finder
- Click your iPhone under "Locations" in the left sidebar.
- Tap “Trust the Device” (if prompted) and enter passcode
- Click “Trust” or “Continue” on your Mac.
- Go to the “General” tab in the Finder window.
- Under Backups, select: "Back up all of the data on your iPhone to this Mac"
- Make sure "Encrypt local backup" is unchecked

If "Encrypt local backup" is checked and greyed out, you'll need to:
- Open Keychain Access (press Command + Space, type “Keychain Access”).
- Search for iPhone Backup or iOS Backup.
- Delete the relevant password.
- Return to Finder and try again.