There are only 2 ways to de-select: 1. click on a blank area of the map, 2. go to the menu > selection tool > clear selection.
(1) works if you are not zoomed in on your map with adjacent boundaries, but if you are then you cannot use this option. (2) technically works but is very inconvenient and not intuitive to users.
There should be another way to de-select without going into the menu. Usually this is done by letting users click on the selected item and this causing the application to clear selection.
