<!-- dropdown -->
<div class="btn-group">
  <a href="#" class="btn btn-default">Dropdown</a>
  <a href="#" class="btn btn-default dropdown-toggle" data-bs-toggle="dropdown">
    <i class="fa fa-caret-down"></i>
  </a>
  <ul class="dropdown-menu dropdown-menu-end">
    ...
  </ul>
</div>

<!-- dropup -->
<div class="btn-group dropup">
  ...
</div>