I added a nav-item dropdown item on the navbar (exactly as specified in the Bootstrap 5 documentation:https://getbootstrap.com/docs/5.0/components/navbar/). It works fine on wider viewports. But once the viewport is small enough that the navbar is collapsed (such as on mobile devices), the dropdown no longer works. Clicking the nav-link dropdown-toggle item doesn't display the dropdown-item elements, but instead closes the navbar menu.

I can only assume that the issue is specific to this theme, since I have another website using vanilla Bootstrap 5 that has no issue with nav-item dropdown elements, and I'm not doing anything differently.