How To Launch Steam Games from Terminal?
To Run on Mac Location:

ll /Users/YOUR_USER_PROFILE/Library/Application\ Support/Steam/steamapps/common/


Command to start a game app directly:

open -Fa /Users/YOUR_USER_PROFILE/Library/Application\ Support/Steam/steamapps/common/Realm\ Grinder/RealmGrinderDesktop.app/Contents/MacOS/RealmGrinderDesktop 


Details

man open


  -F  Opens the application "fresh," that is, without
           restoring windows. Saved persistent state is
           lost, except for Untitled documents.
  
  -a application
           Specifies the application to use for opening the
           file


How To Find Your (Game) Path:

Note: * lines are hyperlinks to images.


Open the Steam App
Navigate to Library *
Right Click on your game.
Open Properties
Navigate to the 3rd Tab Local Files *
Select Browse Local Files
Right Click on the GameName.App
Select Get Info *
Left Click &amp; Drag on the Where
Right Click and select Copy *
Open your text editor and Paste


That will give you the path.


Open Terminal
Add open -Fa ToYourCopiedPath 
Press Return/Enter
Your app will launch.