Hello Harvliet Dalgety !

In Protean template this menu appears by the JQuery function. So if you don't want to use another template then you need to simulate "the initial click" before the page loading. Then you need to add the following code to Studio->Designer->Injection->Head area:

<script>

$(document).ready(function () {

        bx_menu_slide_inline('#bx-sliding-menu-sys_site', $('#bx-menu-toolbar-item-main-menu a').first(), 'site');

    });

</script>