My available space is more than my capacity???

DeltaMac

macrumors G4
Jul 30, 2003
10,246
2,689
Delaware
That's because of your purgeable space.
Purgeable files are actually taking space on your drive, but your system will remove them if the system needs that space for another purpose.
Think of purgeable storage as things that can be re-downloaded. Files stored in iCloud, dictionaries you haven’t used recently, large font files, movies and TV shows you’ve watched, and photos and videos synced with iCloud Photo Library if Optimize Mac Storage is turned on.
Your example is a bit unusual, I think --- purgeable space is larger than your actual space used.

Do a short bit of math. Subtract Purgeable from Total Available. You get 447.60 GB
Add your Used to that amount. That results in 510.89 GB -- approximately your actual capacity (slightly off from that, probably because of rounding, but close enough to show you that the Purgeable amount is the difference.
 
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