I used OmniDiskSweeper as shown and not only do disk utility and system settings don't match in terms of what they say is my free space, but it's completely inconsistent they are both incorrect! How do I fix it???
Open DiskWave and go to the preferences.
Put a checkmark in "show invisible files".
Close preferences.
The DiskWave window shows you all your volumes and drives in plain English (no ridiculous graphical formats).
Click on any item "on the left".
Now, you'll see what's ON the volume, listed in order of "largest to smallest".
You can easily locate what's eating up your space.
What is "disk19s1" in the DiskUtility picture? It appears to be another APFS sub-volume of the "Macintosh HD" group. What's the size of that and how did it get there? That could be the difference.
I have been having this same issue. Thank you @iHavequestions for asking this here. It’s so strange. I deleted 230 GB+ of files and the free space in Disk Utility actually decreased from what it said before I deleted files.
I called Apple about this and they had me click on the Apple logo in the top left, then About this Mac, then on the storage tab and there it showed me a much more accurate reading of the free space on my machine. Using the “manage” button on that screen gave me useful tools for searching for and removing large unwanted files.
Apple never explained why there is such a massive differential between Disk Utility and the above method I just mentioned, but it was a huge relief to see that I am actually freeing up space. If others can explain the reason please do. Hope this is somehow helpful anyhow.