Qt 6 breaks compatibility of QVariant streaming into QDataStream

I have a complex QVariantMap data structure and serialize it to QDataStream in one shot as below:
stream << map;

Some values of the data structure are of type PairDouble, which is an alias for QPair<double, double>:
using PairDouble = QPair<double, double>;
Q_DECLARE_METATYPE(PairDouble);

The problem I faced is that my app built with Qt5 and Qt6 produces mutually incompatible files, because the app built with Qt6 prints "QVariant::load: unknown user type with name PairDouble" and the app built with Qt5 outputs "QVariant::load: unknown user type with name std::pair<double,double>".

I suppose that the problem is in making QPair an alias for std::pair (see https://bugreports.qt.io/browse/QTBUG-80309).