Why does this have to be so hard. Just allow for the delete key like every image editor out there?
Welcome to the forum, @Andres_Narvaez!
The delete and backspace keys perform the Edit › Clear command, which paints the selected area with the background color.
Are you trying to clear the selection? Edit › Selection › Select None will do that. Or you an press shift+ctrl+A (shift+cmd+A on macOS).