This code belongs to this article: https://hesam-kamalan.medium.com/flutter-web-download-file-from-firebase-6a5c35ef7613

file_downloader.dart

import 'dart:convert';
import 'dart:html';

Future<void> downloadFile(String fileName, String pathToFile) async {
  if (pathToFile.isEmpty) return;
  if (!kIsWeb) return;

  Uint8List? data = await FirebaseStorage.instance.ref(pathToFile).getData();
  if (data == null) return;
  String encodedData = base64Encode(data);

  try {
    html.AnchorElement(href: 'data:application/octet-stream;charset=utf-8;base64,$encodedData')
      ..setAttribute('download', fileName)
      ..click();
  } catch (error) {
    print(error);
  }
}