Hi krisk_
Welcome to the Apple (user-to-user) Community.
Wondering which MacBook Air Model you are using:
How to: Identify your MacBook Air model – Apple Support
Re: Where the difference come from?
Seems the best, most accurate estimate of storage space on macOS Ventura is:
Apple menu > System Settings,
click General in the sidebar, then click Storage on the right.
Other estimates may or may not include such things as "temporary files" etc., that can be deleted by the sytem if space is short.
NB: Items in the trash are likely to be included in all estimates, and, if deleted,
may also continue to be included until Mac is restarted.
Best first step is always to back up everything, before deleting anything.
Then valuable documents etc., can always be retrieved / restored.
How to: Free up storage space on your Mac – Apple Support
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Re: Do you have solid solution to freeing space on your mac's
(how to identify where the bulk of heavy file are).
How to: Optimise storage space on your Mac – Apple Support
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More info:
Older discussion thread with:
good info on storage,
a link to find more about what “other”storage contains, and:
scroll to the difference between “free Space” and “available space” from etresoft.
How much space is really available on my … - Apple Community
All the best :-)