onTapOutside property
Fires when the user taps the scrim (the dim area outside the captured rect). Lives on the scrim's own GestureDetector, not Stage's TapGestureRecognizer, so it doesn't compete in the gesture arena with GestureDetectors inside the captured widget tree. Pair this with no onTap when the captured widget hosts its own interactive children that need to win their taps.
Implementation
final VoidCallback? onTapOutside;