QFileDialog::getSaveFileName does not show extension in filter

Question

Qt 6.6.0 in Ubuntu 23.10. Here my short code:

QSettings settings;
QDir defaultDir(settings.value("Default path", QDir::home().absolutePath()).toString());
QString filter = "SQL Database (*.sql)";
QString file = QFileDialog::getSaveFileName(this, tr("New file"), defaultDir.path(), filter, &filter);

It actually works, but the filter in the file dialog does not show the extension:

I would like to show also (*.sql). I tried some hacks, like:

QString filter = "SQL Database (*.sql) (*.sql)";

or

QString filter = "SQL Database \(*.sql\) (*.sql)";

but none works. What is the right syntax in order to show the extension in the file dialog?