Scissors

The Scissors tool can be used to cut away lines from an existing vector shape. Select an existing shape and select the Scissors icon in the toolbar or use Layer › Paths › Scissors for the menu bar.

You can then click on a line in your vector shape to cut it away. When you’re finished, click outside the shape or press Enter/Escape to exit the scissors tool. When there is only a single line left, you’ll leave the Scissors tool automatically.