Troubleshooting & messages · Permissions and Full Disk Access
Why doesn't Storage Studio's breakdown add up to my whole disk?
Short answer: Storage Studio measures what it can read; the remainder is macOS itself, protected system areas and space held in automatic backups. It labels that rather than guessing.
Storage Studio measures what it can see, mostly your home folder. The rest of the used space is macOS itself and system areas no app is allowed to read — plus space your Mac is holding in automatic backups (local snapshots). It labels that remainder rather than guessing what's in it.
To see how much your Mac is holding in local snapshots, use the Local Snapshots section. See System Data.