InvenTree/InvenTree/templates/sidebar_toggle.html

<a href="#" id='sidebar-toggle' class="list-group-item sidebar-list-group-item border-end-0 d-inline-block text-truncate sidebar-toggle" data-bs-parent="#sidebar" style='display: none;'>
    <i class="bi bi-bootstrap"></i><span id='sidebar-toggle-icon' class='sidebar-item-icon fas fa-chevron-left'></span>
</a>