There is a Difference between " Purgeable Storage " and " Empty Space " on the Internal Drive.
Purgeable Storage is managed by the Operating System.
It will be eventually released back as Empty Space when the Operating System decides the space is needed for repurpose
The Repurpose can even become Empty Space and may take a day or two before it become available again Empty Space.
Rebuild the Spotlight index on your Mac
What is “Other” storage on a Mac, and how can I clean it out?
Free up storage space on your Mac
OmniDiskSweeper Safe to use
GrandPerspective
How to delete Time Machine snapshots on your Mac
See used and available storage space on your Mac
Locate backups of your iPhone, iPad, and iPod touch
Notation - If the user is using a cloning software like Carbon Copy Cloner - suggest tweaking the Safety Net Feature in this software. It may be making additional Snap Shots that are not being Cloned to the Eternal Drive. If this should be the case, these Snap Shot could be using additional space on the drive
The final word from Apple on Managing the " Other/ System Data “ Category
Other / System Data: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.
Addition as pervious contributor @ Old Toad mentioned.
RAM = Random Access Memory
Storage = the Total Drive Capacity which appears from the above to be a 256 GB Drive Capacity