I have got an error when i ported Smarty via Composer autoload. "autoload": { "psr-4": { "Smmarty\\": "src/libs/smarty/smarty/src/", ..... } }, so, i guess this way ...

Looking at the code, in the get_main_tabs_for_page_with_tabs() function on class-menu-manager.php file, pages are fetched by slug using the get_page_by_slug ...