MainWindow.blp

using Gtk 4.0;
using Adw 1;

template $ExampleWindow: Adw.ApplicationWindow {
  title: 'Python - PyGObject - GTK';
  default-width: 683;
  default-height: 384;
  width-request: 500;
  height-request: 300;

  Adw.Breakpoint {
    condition ('max-width: 550')

    setters {
      switcher_bar.reveal: true;
      header_bar.title-widget: title_widget;
    }
  }

  content: Adw.ToastOverlay {
    child: Adw.ToolbarView {
      [top]
      Adw.HeaderBar header_bar {
        title-widget: Adw.ViewSwitcher {
          stack: stack;
          policy: wide;
        };
      }

      content: Adw.ViewStack stack {
        Adw.ViewStackPage {
          name: 'page01';
          title: 'Python - PyGObject - GTK';

          child: Gtk.Box {
            orientation: vertical;
            margin-top: 12;
            margin-end: 12;
            margin-bottom: 12;
            margin-start: 12;
            spacing: 12;

            Label {
              label: 'Page 01';
            }
          };
        }

        Adw.ViewStackPage {
          name: 'page02';
          title: 'Python - PyGObject - GTK';

          child: Gtk.Box {
            orientation: vertical;
            margin-top: 12;
            margin-end: 12;
            margin-bottom: 12;
            margin-start: 12;
            spacing: 12;

            Label {
              label: 'Page 02';
            }
          };
        }
      };

      [bottom]
      Adw.ViewSwitcherBar switcher_bar {
        stack: stack;
      }
    };
  };
}

Label title_widget {
  label: 'Python and GTK: PyGObject libadwaita Adw.ViewStack';
}