The answer could be anything from 15 to 32 GB. Maybe the Finder’s just having a wild guess? Numbers courtesy of Big Sur and APFS.
APFS
Extends support for the new feature in Big Sur to make Time Machine backups to APFS volumes.
Volume layouts are fairly straightforward until you have two or more bootable systems with Volume Groups. Details and advice for those with macOS 10.15 or 11.
All about xattrs: their origin, where they’re stored, how they’re named and typed, how to find and work with them, and their common problems.
Explaining inodes, names, dates, permissions, file types, and specialised attributes used for iCloud.
Looking in more detail at newer tricks used by APFS on the data of files: sparse files, which can squeeze vast empty files almost to nothing; file clones; and compression, opening up in Big Sur.
Disk structure diagrammed for comparison, from the partition table, to HFS+ and APFS volumes, with further references.
What you need to know about the APFS file system, its containers and volumes, so you can understand errors and how to repair them.
What you need to know about the HFS+ file system, so you can understand error reports and how to repair it using Disk Utility and other tools.
What you need to know about disk formatting using the GUID Partition Table (GPT) to understand its problems and how to repair it.
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