In Android, capturing WebView content works fine, but on iOS, it captures a blank screen. Is there a solution for this?

Code sample

/// UI
           RepaintBoundary(
                        key: chartContainerKey,
                        child: Container(
                          color: Colors.transparent,
                          child: Center(
                            child: Column(
                              children: <Widget>[
                                SizedBox(
                                  width: isPortrait ? (tabletLayout ? 400.h : 310.h) : (tabletLayout ? 800.h : 400.h),
                                  height:
                                      isPortrait ? (tabletLayout ? 430.h : 335.h) : (tabletLayout ? 310.h : 410.h),
                                  child: Echarts(
                                    key: ValueKey(DateTime.now()),
                                    extensions: const [glScript],
                                    captureAllGestures: true,
                                    onLoad: (p0) {
                                      print('로딩 완료');
                                      // resizeChart();
                                    },
                                    option: '''
                                      {
                                        graphic: [
                                        {
                                              type: 'text',
                                              z: 40,
                                              top: '97%',
                                              left: '4%',
                                              ....
                                              ....

/// capture
Future<bool> captureGraph() async {
  try {
    PermissionStatus ps = await Permission.photos.request();
    if (ps.isPermanentlyDenied) {
      noticeDialog(
          context: context,
          contents: "앱 설정에서 블루투스 권한을 허용해주세요.",
          onPressed: () async {
            await openAppSettings();
          });
      return false;
    }

    RenderRepaintBoundary boundary = chartContainerKey.currentContext!.findRenderObject() as RenderRepaintBoundary;
    ui.Image image = await boundary.toImage(pixelRatio: 3.0);
    ByteData? byteData = await image.toByteData(format: ui.ImageByteFormat.png);
    Uint8List pngBytes = byteData!.buffer.asUint8List();
    final result = await ImageGallerySaver.saveImage(Uint8List.fromList(pngBytes));
    print(result);
    
    return true;
  } catch (e) {
    print("Error capturing screen: $e");
    return false;
  }
}

Expected results
The capture includes the graph. (The results obtained on Android.)

enter image description here

Actual results
The capture is successful, but the graph appears as a white screen. (The results obtained on iOS.)

enter image description here