It's enabled by default in qt6

kcolorchooser.cpp

@@ -40,8 +40,10 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 int main(int argc, char *argv[])
 {
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling, true);
     QCoreApplication::setAttribute(Qt::AA_UseHighDpiPixmaps, true);
+#endif
     QApplication app(argc, argv);
 
     KLocalizedString::setApplicationDomain("kcolorchooser");