Excessive storage displaying in finder

This data is cached. If the caches become stale, the displayed data will drift. Boot into Safe Mode to rebuild the caches, and see if the usage displays resolve.

How to use safe mode on your Mac - Apple Support

Toggle on hidden file viewing within Finder, and see if that accounts for the difference. Command-Shift-Period.

System data is what macOS uses for itself, and that varies by what then users and the apps involved are doing.

Safe Mode reboot can rebuild what’s cached, but the caches usually then resume.

A Mac that’s tight in storage will usually need manual storage management, unfortunately.

So that I understand what is confusing or is skewed… I see two-thirds of a gigabyte shown in your first display. Are you summing what’s shown underneath that, or looking at something else?