Where have all my disk GB gone?

@ dalchina,
I cannot edit the thread title. I''ll post another one later (maybe titled (Discrepancies in disk space usage reported in "Properties"?). The thread title was a weak pun, based on the song "Where have all the flowers gone?".

@ selden,
Pagefile is automatically managed
I have no Universal software (unless any came pre-installed by Acer)

@ Helmut,
My screenshot showing 62.5 GB usage seems OK to me. The title at the top says swapfile.sys, ... Properties (my emphasis of the ...) and the Type is "Multiple files". The Explorer view shows that swapfile.sys itself is 262,144 KB.

I will wait for the auto-delete of Windows.old and report back.

I'm back
After a while, the Windows.old folder has been auto-deleted. But there is still a discrepancy between
(a) the "Used space" as shown in Properties for C: and
(b) the "Size on Disk" as shown on Properties for all the folders and files on C: (including hidden and system-protected ones).

With some more investigation and Googling around, I think that the discrepancy is explained by:
-- the disk space used for System Restore Points (in C:/System Volume Information) is counted in (a) but not in (b)
-- the disk space used for C:/Program Files/WindowsApps is counted in (a) but not in (b)

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Investigation Details:
Running the command "vssadmin list shadowservice" lists three figures - disk space used, disk space allocated and maximum disk space. I can not find any explanation of the second figure but is could well be the case that that "allocated" figure is included in (a) but not in (b) (it is bigger than the disk space used figure.)

I also saw that the Max space had been automatically set at 10% of the disk size, that it 93GB. In System Restore, I reduced this to a (more sensible, imo) 30 GB. Slightly oddly, that deleted my 2 System Restore Points, even though they only used 3 GB.

WindowsApps is reported as an empty folder in Explorer, but the sizes of the Apps can be seen in Settings / Apps & Features. Norton Security scanned 71,000 files in the WindowsApps folder.

Two of the three programs that I installed (Foxit Reader and Acronis true Image are listed as Apps with their disk space usage shown); they do not appear in their own folders in C:/Program Files/.... The third program (Reaper DAW) is also listed as an App, but without a disk space figure; it does have its own folder in C:/Program Files/....

The anomaly in Firefox (it was pre-installed, but I have updated it to the latest version): it is listed as an App with used disk space of 206 MB AND it it is in C:/Program Files with that same disk space. I wonder why