Bad performance of QDateTime::toMSecsSinceEpoch() in Qt 6

QDateTime::toMSecsSinceEpoch() costs at least ten times  of computation resource in Qt 6 series than Qt 5 series.

It's performance is worse when compared to standard library implemention like

std::chrono::duration_cast<std::chrono::milliseconds>(time_point.time_since_epoch()).count();