Create new project with any Qt version and enter the next sample program

#include <QCoreApplication>
#include <QXmlStreamReader>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    QXmlStreamReader reader;
    
    return a.exec();
}

QXmlStreamReader is not highlighted and there's no autocompletetion of methods for reader variable. However, parser recognizes QXmlStreamReaderPrivate.