Apple - macOS not showing the actual free space

You probably have some local snapshots on your drive, you can try to list the local snapshots with

tmutil listlocalsnapshots /

and with

tmutil thinlocalsnapshots / 9999999999 1

you can delete all local snapshots and release the storage space.

You can find more information here How to thin your local Time Machine Snapshots on macOS High Sierra

Commands given below resolved the issue for me. Listed and deleted local snapshot and it freed 230 GB on my machine.

$ tmutil listlocalsnapshots /
com.apple.TimeMachine.2019-01-28-143406 
$ tmutil deletelocalsnapshots 2019-01-28-143406  
$ tmutil listlocalsnapshots /
$

Make sure it shows no file at the end.