Unable to get file icon by QFileIconProvider()

When I migrating my project from QT5.15.2 to QT6.0.2, I found that QFileIconProvider return null in QT6.0.2 but return file icon in QT5.15.2, so I write a small project to test it.

simple code here:

QPixmap FrmMain::GetICON(const QString &path) {
  QFileIconProvider provider;
  auto icon = provider.icon(QFileInfo(path));
  return icon.pixmap(icon.availableSizes().last());
}

This function return file icon in QT5.15.2, but return null in QT6.0.2.