Follow the previous advise - First
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.
There are areas of the Operating System which we users have control over and that is the User Account Folder ( Home Folder )
It is generally a good computer practice to alway keep at least 20% to 25% of the Total Drive Capacity’s as Empty Space. Allowing the computer to drop below these guidelines may eventually, cause unintended consequences.
There is Purgeable Space and there is Empty Space.
Purgeable Space which is Controlled by the Operating System. When the Operating Systems decides the computer needs additional Empty Space, it will move a portion of the Purgeable to Empty space
AFAIK - there is no User Actions to hasten this transition from Purgeable to Empty Space
It can day or longer before this will occur.
The links below will assist in identifying what is taking up space on the Internal Drive and provide possible ways to remove data that is under the direct control of the User ( Home Folder ) .
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
GrandPerspective
