Apple Resources - Screen Sharing
http://edu-observatory.org/olli/Manage/Screen_Sharing.html

Share your screen using Messages on Mac
  https://support.apple.com/guide/messages/screen-sharing-icht11883/mac   
Share the screen of another Mac
  https://support.apple.com/guide/mac-help/share-the-screen-of-another-mac-mh14066/mac   
  https://support.apple.com/guide/mac-help/turn-screen-sharing-on-or-off-mh11848/mac   

  One important capability available to Mac owners is the
  ability to screen share between any two Mac computers over
  the internet. With the permission of both parties the
  initiator can share remote owner's screen, sound and cursor
  function.
  
Siri "Open  Screen  Sharing"

From the Terminal
  open -a Screen\ Sharing.app

  

From Messages

  

     
  
  

 
    sam.wormley@icloud.com