You click once then you can start scrolling wheel it will make blue lines to cover the opening. Once the lines touch fill will work. If you press s to change from extend to radius it will have red circles until you make them large enough to close the gap. At that point it will change to a blue line. I’m still learning how to draw and learning grease pencil. I saw the options on the status bar one day and started playing with that. For me it’s easy because I use to have 28 version of Blender. I have it down to 14 now. Although the 2 Blender for artists versions some people don’t count.
