It's enabled by default in qt6

src/app/main.cpp

@@ -212,9 +212,10 @@ int main(int argc, char **argv)
     QCoreApplication::setOrganizationName(QStringLiteral("KDE"));
     QCoreApplication::setOrganizationDomain(QStringLiteral("kde.org"));
     QCoreApplication::setApplicationVersion(QStringLiteral(ITINERARY_VERSION_STRING));
-
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
     QGuiApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+#endif
 #ifdef Q_OS_ANDROID
     QGuiApplication app(argc, argv);
     QQuickStyle::setStyle(QStringLiteral("Material"));