How to add widget to appear only when sharing to social - flutter

Question

I tried share package and it works but I want to add a Widget that only appears on the shared image, not on the app. So please help me this is the code so far:
import 'dart:ui';
import 'dart:io';
import 'package:path_provider/path_provider.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:share/share.dart';
void main() {
runApp(MaterialApp(home: HomePage()));
}
class HomePage extends StatelessWidget {
final _contentKey = GlobalKey();
final bool forSharing;
HomePage({
Key key,
this.forSharing = false,
}) : super(key: key);
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
actions: [
IconButton(
icon: const Icon(Icons.share),
onPressed: () => onTakeScreenShotAndSharing(
'Image',
_contentKey.currentContext,
),
),
],
),
body: RepaintBoundary(
key: _contentKey,
child: Column(
children: [
if (forSharing) Text('Text appear only for Sharing'), // This is the widget that I want it appear only on the shared image
Text('Content'),
],
),
),
);
}
void onTakeScreenShotAndSharing(String fileName, BuildContext context) async {
try {
RenderRepaintBoundary boundary = context.findRenderObject();
final image = await boundary?.toImage();
final bytes = await image?.toByteData(format: ImageByteFormat.png);
if (bytes == null || bytes.buffer == null) return;
final dir = (await getApplicationDocumentsDirectory()).path;
final file = File('$dir/$fileName${DateTime.now().toString()}.png');
final newFile = await file.writeAsBytes(bytes.buffer.asUint8List());
await Share.shareFiles([newFile.path]);
} catch (error) {
print(error);
}
}
}