How to recycle some magnetic disk of System on Mac OS?
Your system storage space is more than usual.

Cache files can take up a lot of space. 

How to remove them:

From Mac Paw


  Open a Finder window and select Go in the  menu bar.
  
  Click on “Go to Folder…”
  
  Type in ~/Library/Caches. Delete the files/ folders that are taking
  up the most space.
  
  Now click on “Go to Folder…”
  
  Type in /Library/Caches (simply lose the ~  symbol) And, again, delete
  the folders that  take up the most space.


Another thing that could help is starting in safe mode.

From this Apple Discussion:


  Try this...
  
  Start your mac in Safe mode by holding the shift key before the power
  key
  
  Check your storage About This Mac/Storage etc. (In safe mode, mine
  showed accurate usage) 
  
  Restart in normal mode
  
  Repeat step #2.