A_MacBook_Pro_512G_Owner wrote:
System data, cannot be accessed, cannot be deleted, yet still occupying hundreds of Gs.
You can’t directly manage the contents of this category. That is done by macOS. The category varies in size depending on the current state of your Mac.
What you can do…
• Empty the Trash in the Dock.
• Empty the trash in the Photos app.
• Delete unused and unneeded application installers from your downloads folder and desktop.
• Reboot your Mac at least weekly.
• Transfer files that you don’t use daily to an external drive and then delete them from the startup drive and empty the trash. Files that take up the most room are movies, images and music.
This from Apple on the subject of freeing up space:
Free up storage space on Mac - Apple Support
Also, please see the following guidance from Apple:
Find and delete files on your Mac - Apple Support
[...]
My classmate told me I she had encountered the same problem, took her MacBook back to Apple, and they solved her issue for a price.
Did your classmate tell you how Apple solved the problem?
I suspect they simply wiped the drive and reinstalled macOS.
How to reinstall macOS - Apple Support