I have read your description and compared the storage information of my MacBook Pro, then I find that the missing portion of your Mac is not reported. The missing part is the system data running your Mac computer. If you want to make it clear, you can rely on a third-party tool -- iBoysoft DiskGeeker, which analyzes the hard drive space and lists all system data.
Feel free to download and install iBoysoft DiskGeeker to analyze the system data stored on your Mac right now!