Freeing up space · What's Using Space (Storage Inspector)
Why does What's Using Space mark a folder as unreadable?
Short answer: macOS won't let Storage Studio read that folder, so its size can't be measured. It's labelled unreadable instead of being counted as empty; granting Full Disk Access usually fixes it.
It means macOS won't let Storage Studio look inside that folder, so its size can't be measured. Storage Studio labels it unreadable rather than silently counting it as empty, so you aren't misled about where your space is.
The most common fix is to make sure Storage Studio has Full Disk Access in System Settings → Privacy & Security; without it, many personal folders are off-limits. Some areas are closed to every app regardless, and the footer notes that too.
See the Getting started FAQ for granting Full Disk Access.