Macintosh HD says almost full but folder sizes don't add up... why?

Using Big Sur 11.4 on 16" MBP 2019 with 4TB drive. Get Info on Macintosh HD (the only drive I have) says 545GB remaining of 4TB drive. The 4 folders on the root of the drive are listed below with respective file sizes that show in Get Info:

Applications - 67.2 GB

Library - 23.15 GB

System - 26.24 GB

Users - 2.71 TB

The total is about 2.83 GB, that leaves 1.17 GB remaining on the drive though some is surely taken up by the system OS. But that is HUGE gap between the 1.17 GB that should be remaining vs the 545 GB that the system tells me is remaining. TechToolsPro is continually warning that I'm running out of drive storage because I had it set to notify me at 15% remaining.

Why this discrepancy and is there actually free space I can somehow reclaim?