Save images in a custom folder in the gallery - flutter

Question

Im new at Flutter and im trying to add images taken in my app to a custom folder in the gallery. Its the same as on WhatsApp, if you take a picture in a chat the WhatsApp create a custom folder called WhatsApp Images.
For that, I tried this:
Future<bool> saveFile(String url, String fileName) async {
Directory directory;
try {
if (Platform.isAndroid) {
if (await _requestPermission(Permission.storage)) {
directory = (await getExternalStorageDirectory())!;
String newPath = '';
List<String> folders = directory.path.split('/');
for (int x = 1; x < folders.length; x++) {
String folder = folders[x];
if (folder != 'Android') {
newPath += '/$folder';
} else {
break;
}
}
newPath = '$newPath/OnlaineApp';
directory = Directory(newPath);
} else {
return false;
}
} else {
if (await _requestPermission(Permission.photos)) {
directory = await getTemporaryDirectory();
} else {
return false;
}
}
if (!await directory.exists()) {
await directory.create(recursive: true);
}
if (await directory.exists()) {
File saveFile = File('${directory.path}/$fileName');
await dio.download(url, saveFile.path,
onReceiveProgress: (downloaded, totalSize) {
setState(() {
progress = downloaded / totalSize;
});
});
if (Platform.isIOS) {
await ImageGallerySaver.saveFile(
saveFile.path,
isReturnPathOfIOS: true,
);
}
return true;
}
} catch (e) {
print(e);
}
return false;
}
Future<bool> _requestPermission(Permission permission) async {
if (await permission.isGranted) {
return true;
} else {
var result = await permission.request();
if (result == PermissionStatus.granted) {
return true;
} else {
return false;
}
}
}
downloadFile() async {
setState(() {
loading = true;
});
bool downloaded = await saveFile(
'lib/assets/images/fundo_interno.png',
'OnlaineApp Imagens',
);
if (downloaded) {
print('File downloaded');
} else {
print('Problem downloaded file');
}
setState(() {
loading = false;
});
}
I already add in Android>app>src>main> AndroidManifest.xml these lines of code (for permission):
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
...
android:requestLegacyExternalStorage="true"
The problem I got is: I/flutter ( 5424): FileSystemException: Creation failed, path = '/storage/emulated/0/OnlaineApp' (OS Error: Permission denied, errno = 13)