Files that are hidden from view but still occupy disk space

This usually happens because the space is being used by system or protected files that File Explorer doesn’t show by default, or by data that’s stored outside your user folders.

I’d check a few things first:

• In File Explorer, go to View > Show > Hidden items to display hidden files.
• Open Folder Options > View and temporarily uncheck “Hide protected operating system files (Recommended)”. Be careful not to delete anything unless you’re sure what it is.
• Go to Settings > System > Storage and review the storage categories. They often point you to large folders, temporary files, Windows Update cleanup, or system files.
• Run Disk Cleanup (or Storage Sense) to safely remove temporary files, Windows Update leftovers, and other unnecessary data.

If you’re still missing hundreds of gigabytes after that, the space may be used by things like:

• System Restore points or Shadow Copies
• The page file (pagefile.sys) or hibernation file (hiberfil.sys)
• Virtual machine images 
• Hidden application data under ProgramData or AppData

If you can share which version of Windows you’re using and whether the missing space is on an HDD or SSD, it will be easier to narrow down the cause.