Can be used to enable touch events to happen in a Positioned widget which is outside of the stack boundaries.

positioned_overlay_entry.dart

class PositionedOverlayEntry extends StatefulWidget {
  final OverlayState overlay;
  final Widget child;
  final double? left;
  final double? top;
  final double? right;
  final double? bottom;
  final double? width;
  final double? height;

  const PositionedOverlayEntry({
    Key? key,
    required this.overlay,
    this.left,
    this.top,
    this.right,
    this.bottom,
    this.width,
    this.height,
    required this.child,
  }) : super(key: key);

  @override
  _PositionedOverlayEntryState createState() => _PositionedOverlayEntryState();
}

class _PositionedOverlayEntryState extends State<PositionedOverlayEntry> {
  late final OverlayEntry _overlayEntry;
  final _childKey = GlobalKey();
  Offset? _topLeft;
  Offset? _bottomRight;

  @override
  void initState() {
    super.initState();
    _overlayEntry = OverlayEntry(builder: _overlayBuilder);
    WidgetsBinding.instance!.addPostFrameCallback((_) {
      _measure();
      widget.overlay.insert(_overlayEntry);
    });
  }

  @override
  void dispose() {
    _overlayEntry.remove();
    super.dispose();
  }

  void _measure() {
    final stackRenderBox = context.findRenderObject()!.parent as RenderBox;
    final overlayRenderBox =
        widget.overlay.context.findRenderObject() as RenderBox;

    Offset stackToOverlay(Offset offset) {
      return overlayRenderBox
          .globalToLocal(stackRenderBox.localToGlobal(offset));
    }

    var topLeft = Offset.zero;
    topLeft = stackToOverlay(topLeft);

    var bottomRight = Offset(
      stackRenderBox.size.width,
      stackRenderBox.size.height,
    );
    bottomRight = stackToOverlay(bottomRight);
    bottomRight = Offset(
      bottomRight.dx - overlayRenderBox.size.width,
      bottomRight.dy - overlayRenderBox.size.height,
    );

    setState(() {
      _topLeft = topLeft;
      _bottomRight = bottomRight;
    });
  }

  Widget _buildChild(BuildContext context) {
    return KeyedSubtree(
      key: _childKey,
      child: widget.child,
    );
  }

  Widget _overlayBuilder(BuildContext context) {
    double? top;
    double? left;
    double? bottom;
    double? right;
    if (widget.top != null) top = widget.top! + _topLeft!.dy;
    if (widget.left != null) left = widget.left! + _topLeft!.dx;
    if (widget.bottom != null) bottom = widget.bottom! - _bottomRight!.dy;
    if (widget.right != null) right = widget.right! - _bottomRight!.dx;

    return Positioned(
      top: top,
      left: left,
      bottom: bottom,
      right: right,
      width: widget.width,
      height: widget.height,
      child: _buildChild(context),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Positioned(
      left: widget.left,
      top: widget.top,
      right: widget.right,
      bottom: widget.bottom,
      width: widget.width,
      height: widget.height,
      child: _topLeft == null ? _buildChild(context) : SizedBox(),
    );
  }
}