Now it depends against new version. Old code can be removed

src/kcm.cpp

@@ -52,13 +52,8 @@ K_PLUGIN_FACTORY_WITH_JSON(KCMPlymouthFactory, "kcm_plymouth.json", registerPlug
 KCMPlymouth::KCMPlymouth(QObject* parent, const QVariantList& args)
     : KQuickAddons::ConfigModule(parent, args)
 {
-#if (QT_VERSION < QT_VERSION_CHECK(5,14,0))
-    qmlRegisterType<QStandardItemModel>();
-    qmlRegisterType<KCMPlymouth>();
-#else
     qmlRegisterAnonymousType<QStandardItemModel>("KCMPlymouth", 1);
     qmlRegisterAnonymousType<KCMPlymouth>("KCMPlymouth", 1);
-#endif
     KAboutData* about = new KAboutData(QStringLiteral("kcm_plymouth"), i18n("Boot Splash Screen"),
                                        QStringLiteral(PROJECT_VERSION), QString(), KAboutLicense::LGPL);
     about->addAuthor(i18n("Marco Martin"), QString(), QStringLiteral("mart@kde.org"));