it's removed in qt6

src/main.cpp

@@ -10,8 +10,9 @@
 #include <KCrash>
 #include <KLocalizedString>
 #include <KDBusService>
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 #include <Kdelibs4ConfigMigrator>
-
+#endif
 #include <QApplication>
 #include <QUrl>
 #include <QCommandLineParser>
@@ -31,11 +32,12 @@ int main(int argc, char** argv)
 #endif
     QApplication app(argc, argv);
     KLocalizedString::setApplicationDomain("knavalbattle");
-
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     Kdelibs4ConfigMigrator migrate(QStringLiteral("knavalbattle"));
     migrate.setConfigFiles(QStringList() << QStringLiteral("knavalbattlerc"));
     migrate.setUiFiles(QStringList() << QStringLiteral("knavalbattleui.rc"));
     migrate.migrate();
+#endif
 
     KAboutData aboutData(QStringLiteral("knavalbattle"), i18n("Naval Battle"),
         QStringLiteral(KNAVALBATTLE_VERSION_STRING),