Galaxy Note 9: Hidden features you can only do with an S Pen – CNET

Save a note for later

If you get started on a note and need to duck out to do something else, you can come back to it by turning it (and many other apps) into a floating icon that you can move around the screen. 

For example, after composing a new note through a shortcut setting, click the icon to minimize the window into the icon you see. Tap to revive.