Flutter Error: Unhandled Exception: FileSystemException: Cannot open file (OS Error: Permission denied, errno = 13) - flutter-dependencies

Question

I'm trying to read and write a json file in device emulator Download folder but i get the error above (Flutter version 3.3.6).
After many attempts and many changes to my android/app/build.gradle I succeded in reading the file (basically i found that it works only if i manually put targetSdkVersion 29) but I still get the permission denied error when i try to write it.
I'm using the permission handler package and I when I run the app in the emulator I'm asked for the storage permission and I grant it.
Here's what my AndroidManifest.xml first lines looks like:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.flutter_application_1">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<application
android:label="flutter_application_1"
android:name="${applicationName}"
android:icon="#mipmap/ic_launcher"
android:requestLegacyExternalStorage="true">
Here's a bit of my android/app/build.gradle :
`android {
//compileSdkVersion flutter.compileSdkVersion
compileSdkVersion 33
ndkVersion flutter.ndkVersion
defaultConfig {
applicationId "com.example.flutter_application_1"
//minSdkVersion flutter.minSdkVersion
//targetSdkVersion flutter.targetSdkVersion
minSdkVersion 21
targetSdkVersion 29
versionCode flutterVersionCode.toInteger()
versionName flutterVersionName
}`
I added the following dependency in pubspec.yaml: permission_handler: ^10.2.0
Here's the part of the code that handles the permissions and the reading/writing methods:
import 'dart:convert';
import 'dart:io';
import 'package:permission_handler/permission_hndler.dart';
Future<bool> requestPermission(Permission permission) async {
if (await permission.isGranted) {
return true;
} else {
var result = await permission.request();
if (result == PermissionStatus.granted) {
return true;
}
}
return false;
}
class FileManager {
Future<String> get directoryPath async {
Directory directory = Directory('/storage/emulated/0/Download');
return directory.path;
}
Future<File> get jsonFile async {
final path = await directoryPath;
return File('$path/big_book.json');
}
void writeJsonFile(List itemsRubrica) async {
if (await requestPermission(Permission.storage)) {
File file = await jsonFile;
await file.writeAsString(jsonEncode(itemsRubrica));
}
}
Future<String> readJsonFile() async {
if (await requestPermission(Permission.storage)) {
File file = await jsonFile;
String fileContent = await file.readAsString();
return fileContent;
} else {
return 'no data';
}
}
}
I prefer not to put here the rest of my code because it's very long and I think it's not related to this error.
What can I do?
Thanks