setting QML2_IMPORT_PATH does not work

I want to use a custom style for the virtual keyboard. I have all neccessary files added into my resources. When i set the path via

qputenv("QML2_IMPORT_PATH", QByteArray("qrc:///keyboards"));

it does not work. When is use

engine.addImportPath(QStringLiteral("qrc:/keyboards"));

my custom style is properly loaded and shows up in the UI.

Here the complete code:

int main(int argc, char *argv[])
{{{}}

    //DEVNOTE: this does not work
    //qputenv("QML2_IMPORT_PATH",QByteArray("qrc:///keyboards"));
    qputenv("QT_IM_MODULE",QByteArray("qtvirtualkeyboard"));
    qputenv("QT_VIRTUALKEYBOARD_STYLE"      , QByteArray("bnr"));

    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication         app(argc, argv);
    QQmlApplicationEngine   engine;

    // DEVNOTE: this works
    engine.addImportPath(QStringLiteral("qrc:/keyboards"));
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}