not a solution but this may help you with your code
$sTopNav = '';
$sItemOpen = '<li class="nav-item[if (class==menu-expand){ dropdown}][if(class=menu-current||class=menu-parent){ parent}]">'.
'<div class="d-flex">'.
'<a class="nav-link[if(class=menu-current){ active}]" href="[url]">'.
'<span>[menu_title]</span></a>'.
'[if (class==menu-expand){'.
'<a class="nav-link-toggle dropdown-toggle hide-arrow ms-auto" href="#" role="button" aria-haspopup="true" aria-expanded="false">
<i class="bi bi-chevron-down"></i>
</a>}]'.
'</div>';
$topNav = show_menu2(
1,
SM2_ROOT + $iMultiLang, // If you have First menu level /en/, /de/ , use: SM2_ROOT + $iMultiLang,
SM2_ALL,
SM2_ALL|SM2_NUMCLASS|SM2_PRETTY|SM2_BUFFER,
$sItemOpen,
'</li>',
'<ul [if(level==0){class="navbar-nav"} else {class="dropdown-menu"}]>',
'</ul>'
);
$topNav = str_replace('class=""', '', $topNav);