82GB of "other" don't appear in OmniDiskSweeper or Freediskspace
The number Grand Perspective shows as &quot;Miscellanous used space&quot; represents the amount of data that Grand Perspective hasn't scanned.
This could be due to you only scanning part of the drive (for example just scanning the home directory for one user, whilst other user's data haven't been scanned), setting a filter or lack of permissions.
If you haven't done so already, I would suggest giving Grand Perspective Full Disk Access and try again. You do this from System Preferences &gt; Security &amp; Privacy &gt; Privacy.
In case it is not due to files that are not scanned, the space could be taken up by file system snapshots - for example made by TimeMachine backups.