It completely works

main.cpp

@@ -1,24 +1,6 @@
-#include "hello_world.hpp"
-#include <gtkmm/application.h>
-#include <gtkmm/builder.h>
-#include <iostream>
-#include <memory>
+#include "app_win_2_back.hpp"
 
 int main(int argc, char *argv[]) {
-    auto app = Gtk::Application::create("org.gtkmm.example");
-
-    const auto menu_model = []() -> Glib::RefPtr<Gio::Menu> {
-        try {
-            const auto builder = Gtk::Builder::create_from_file("menu_bar.ui");
-            return std::dynamic_pointer_cast<Gio::Menu>(builder->get_object("menu"));
-        } catch (const std::exception &e) {
-            std::cerr << e.what() << '\n';
-            return nullptr;
-        }
-    }();
-    if (menu_model == nullptr) {
-        std::cerr << "Menu model object is null. Down-cast failed.\n";
-        return EXIT_FAILURE;
-    }
-    return app->make_window_and_run<learn_gtkmm4::HelloWorld>(argc, argv, menu_model);
+    auto app = gui_to_app::AppWin2Back::create();
+    return app->run(argc, argv);
 }