The Manage button in Storage came in with later macOS's.
information in About This Mac> Storage is often wrong.
Try rebuilding the Spotlight index,
How to rebuild the Spotlight index on your Mac – Apple Support
Move the Macintosh HD (or the name you gave your disk) in to the Privacy panel.
Quit System Preferences.
Open System Preferences> Spotlight> Privacy highlight Macintosh HD and press the minus button.
The mac will start rebuilding the Spotlight index.
Check by clicking on Spotlight in the menubar and enter word, if it is indexing you should see a progress bar.
If re-indexing has not solved your problem then run this app, https://www.omnigroup.com/more
this will give an accurate account of the storage used. When the app has created its overview you can look at
the Users folder in the output and see what each user has stored, you can then delete files from there.
Do not delete any files or folders in any System or Library folders or any files you do not understand.