The maximum height of the dropdown menu
The maximum height of the menu must be at least one row shorter than the height of the app's view. This ensures that a tappable area outside of the simple menu is present so the user can dismiss the menu.
If this property is set above the maximum allowable height threshold mentioned above, then the menu defaults to being padded at the top and bottom of the menu by at one menu item's height.
final double? maxHeight;