Disk space available: Finder shows way less than System Information The Finder currently shows only 81GB available (at the bottom of a folder's window) whereas System Information > Storage shows 455GB available.

Why does the Finder show so much less space available?

FYI: I'm running macOS 10.15.4 on an iMac with a 500GB drive.
I suggest you run DaisyDisk which will do a graphical display of your disk contents. The app is not free but can be used once as a free trial.  This app will map out your entire disk showing where everything is located.  it will take several minutes to completely map your drive.