Flutter Widget allow child to grow / shrink based on userdrag. DragWidget's gesture will be prioritize that it's parents even if parent is scrollable like SingleChildScrollView.

expandable_widget.dart

import 'package:flutter/material.dart';

class ExpandableWidget extends StatefulWidget {
  const ExpandableWidget({
    super.key,
    required this.child,
    required this.dragWidget,
    this.initHeight,
    this.maxHeight,
    this.minHeight,
    this.onScrollChange,
    this.dragWidgetOffset,
    this.dragWidgetPadding = const EdgeInsets.all(8),
  });

  final Widget child;
  final Widget dragWidget;
  final double? initHeight;
  final double? maxHeight;
  final double? minHeight;
  final Offset? dragWidgetOffset;
  final EdgeInsets? dragWidgetPadding;

  final Function(bool isScrolling)? onScrollChange;

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

class ExpandableWidgetState extends State<ExpandableWidget> {
  double _currentHeight = 0, _maxHeight = 0, _minHeight = 0;

  @override
  void initState() {
    _minHeight = widget.minHeight ?? 100; // default min height as needed
    _currentHeight = widget.initHeight ?? _minHeight;
    _maxHeight = widget.maxHeight ?? double.infinity;

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        SizedBox(height: _currentHeight, child: widget.child),
        Positioned(
          bottom: 0 + (widget.dragWidgetOffset?.dy ?? 0),
          right: 0 + (widget.dragWidgetOffset?.dx ?? 0),
          child: Listener(
            onPointerUp: (event) => widget.onScrollChange?.call(false),
            onPointerDown: (event) => widget.onScrollChange?.call(true),
            onPointerMove: (event) {
              _currentHeight += event.delta.dy;

              setState(() {
                _currentHeight = _currentHeight.clamp(_minHeight, _maxHeight);
              });
            },
            child: Container(
              padding: widget.dragWidgetPadding,
              child: widget.dragWidget,
            ),
          ),
        ),
      ],
    );
  }
}