Moving folders · How moving folders works
Why didn't my free space go up after I moved a folder?
Short answer: Usually your Mac's recent snapshots are still holding the space of the moved files. Storage Studio asks macOS to release it after each move, but macOS decides; it normally returns on its own within about a day, or you can release it in Local Snapshots.
Usually because your Mac's own recent snapshots are still holding the space of the files you just moved. The files really are gone from your built-in drive; macOS just hasn't handed the room back yet.
Storage Studio asks macOS to release that space right after a successful move, and tells you when it has measured that your Mac is still holding a meaningful amount. Releasing is a request, not a command — macOS decides — and held space normally comes back on its own within about a day. You can also release it now from the Local Snapshots manager.
If the move itself didn't finish, check the move's status: a failed or waiting move leaves your originals in place.
See Local Snapshots and freeing space.