It's enabled by default in qt6

src/main.cpp

@@ -28,8 +28,8 @@ int main(int argc, char* argv[])
 {
 #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling, true);
-#endif
     QCoreApplication::setAttribute(Qt::AA_UseHighDpiPixmaps, true);
+#endif
 
     // Use QScopedPointer to ensure the QCoreApplication instance is deleted
     // before libraries unload, to avoid crashes during clean-up.