Disk Utility cannot detect a good portion of my storage space
If you want find the free space, there is a third party utility that will show you were it went. This utility does not require installation or your password to use. You can find more information on this utility from the driveinfo website.

Assume your downloads go to the default download folder. You and find the free space by downloading and entering the command given below.

~/Downloads/driveinfo-1.0.3/driveinfo -r disk0


An alternative to driveinfo command would be the macOS command given below.

sudo gpt -r show /dev/disk0


To use the gpt command, you would need to disable System Integrity Protection (SIP).

If you can post the output from either of these commands, then help could be provided on how to recover the missing space.