reduce system storage on MacBook Pro
How do I reduce the amount of system storage on my MacBook ?
The Storage tab is known to report incorrectly. Also check by choosing your Mac HD and "Get Info" (command-i). It may be different. Try rebuilding Spotlight index.
How to rebuild the Spotlight index on your Mac - Apple Support
Some of the space may also be from Time Machine Snapshots.
About Time Machine local snapshots - Apple Support
Download Omni DiskSweeper:
https://www.omnigroup.com/more
DiskSweeper can give you a more accurate read of disk space than Finder or Storage Tab of About this Mac. It can also show you the precise size and location of all your files. It will inventory your disk starting from the files that take up the most space. If you want you can even delete files from OmniDisk Sweeper. But be careful some of the items may be important to your system.
