The .qmlproject file usually defines an enviroment like this:

  Environment {
        QT_QUICK_CONTROLS_CONF: "qtquickcontrols2.conf"
        QT_AUTO_SCREEN_SCALE_FACTOR: "1"
        QT_LOGGING_RULES: "qt.qml.connections=false"
        QT_ENABLE_HIGHDPI_SCALING: "0"
        /* Useful for debugging
       QSG_VISUALIZE=batches
       QSG_VISUALIZE=clip
       QSG_VISUALIZE=changes
       QSG_VISUALIZE=overdraw
       */
    }

This envoirment should also be defined in main.cpp/import_qml_plugins.h

I suggest adding a function to import_qml_plugins.h that is called in main.cpp.
The function would contain the qputenv calls like this:

qputenv("QT_ENABLE_HIGHDPI_SCALING", "0");
qputenv("QT_LOGGING_RULES", "qt.qml.connections=false");

This way main.cpp itself does not have to be touched.