Hi BR_2020,
Good day! This is Jhakesong an Independent Advisor and I will be happy to assist you with this. You mentioned that your storage count doesn't add up when you count it against the actual file sizes of each folders. This usually happens if you have no administrative privileges or if show hidden files is turned off.
To get an accurate picture of your drives file size and which ones are responsible for it, I would suggest download this third party utility call Tree Size. Just pick the free version. It should be fine.
Here is the link: https://www.jam-software.com/treesize_free
Standard Disclaimer: These are links to non-Microsoft websites. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products often classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.
Hope it helps. Have a great day.