I've been trying for several days to understand how the mobile menu works

I tried to assign modules with off-canvas position to the various menus but it doesn't work

trying to understand the default.php, I found the lines

<div id="gkMobileMenu"<?php if($this->API->get('menu_type', 'off-canvas') === 'off-canvas') : ?> class="off-canvas"<?php endif; ?>>
					<span id="static-aside-menu-toggler" class="fas fa-bars"><span class="element-invisible">static-aside-menu-toggler</span></span>
				</div>

<?php if($this->API->get('menu_type', 'off-canvas') === 'off-canvas') : ?>
<i id="close-menu">&times;</i>
<nav id="aside-menu">
<div>
<?php if($this->API->modules('menu_top')) : ?>
<div id="gk-menu-top">
<jdoc:include type="modules" name="menu_top" style="none" />
</div>
<?php endif; ?> <?php $this->asidemenu->loadMenu($this->API->get('menu_name','mainmenu'));
 $this->asidemenu->genMenu($this->API->get('startlevel', 0), $this->API->get('endlevel',-1));
 ?> <?php if($this->API->modules('menu_bottom')) : ?> <div id="gk-menu-bottom"> <jdoc:include type="modules" name="menu_bottom" style="none" /> </div> <?php endif; ?> </div> </nav> <?php endif; ?>

As far as I can tell, I assume this is the mobile menu

If I examine the html I actually find

<nav id="aside-menu" class="menu-open">
<div class="aside-menu-inner">
<div class="aside-menu-wrap">
<div class="gkAsideMenu">
<ul class="gkmenu level0"><li class="first"><a href="http://mysite.com/" class=" first">Home</a></li></ul>
</div>
<div class="gkAsideMenu">
<ul class="gkmenu level0"><li class="first"><a href="http://mysite.com/" class=" first">Home</a></li></ul>
</div> </div>

</div>
</nav>

I have only "Home" as menu item, how can I make this menu take the same menu items that are seen in desktop mode?

Thanks