How to inject an event like button press programmatically in gtkmm C++?

I am very new to C++ gtkmm (Linux) programming. I developing a program where I need a button to be clicked in the callback function of another button on the gui. I have tried button.activate() But it only animates the button click but the callback function is not called. When I click the button manually, the callback function is called. Please explain how to inject event into the gtkmm C++ coding. Events may include button press, key press etc.

Here is an example that works with Gtkmm 3.24 for a button click:

#include <iostream>
#include <gtkmm.h>

class MainWindow : public Gtk::ApplicationWindow
{

public:

    MainWindow();

private:

    Gtk::Grid m_layout;

    Gtk::Label m_label;

    Gtk::Button m_buttonA;
    Gtk::Button m_buttonB;

};

MainWindow::MainWindow()
: m_buttonA{"A"}
, m_buttonB{"B"}
{
    m_label.set_text("Click a button...");

    m_buttonA.signal_clicked().connect(
        [this](){
            std::cout << "Button A clicked!" << std::endl;

            // Emits "clicked" on button B, just like when
            // a user clicks it:
            m_buttonB.clicked();
            m_buttonB.activate_action("clicked");
        }
    );

    m_buttonB.signal_clicked().connect(
        [this](){
            std::cout << "Button B clicked!" << std::endl;
        }
    );

    m_layout.attach(m_buttonA, 0, 0, 1, 1);
    m_layout.attach(m_buttonB, 1, 0, 1, 1);

    add(m_layout);
}

int main(int argc, char *argv[])
{
    std::cout << "Gtkmm version : " << gtk_get_major_version() << "."
                                    << gtk_get_minor_version() << "."
                                    << gtk_get_micro_version() << std::endl;

    auto app = Gtk::Application::create(argc, argv, "org.gtkmm.examples.base");
  
    MainWindow window;
    window.show_all();
  
    return app->run(window);
}

With Gtkmm 4 however, the clicked() method seems to have been removed from Gtk::Button's interface. By looking at the new interface, there is a activate_action method (inherited from Gtk::Widget) that, maybe, could work. However, I don't have Gtkmm 4 here, so I could not try it.