Depending on where you look for information the results may vary.
Via 'About this Mac' in the menu Finder the panel that makes an
appearance then, offers several items; the Storage would show all
the bits and pieces used by all system parts including partitions.
Or Disk Utility can show you a different aspect of how storage is used.
Some information from Activity Monitor can reflect another viewpoint.
And IF you can see the hard drive icon on the desktop, use Get Info
to see how that lets you see another perspective.
Each vintage or series of operating system has differences; and these
also affect how you can view them. And too if you had Etrecheck utility
that can be run and generate a report, that also shows you more if you
have a paid version. The report may also be posted in your discussion.