How to know if there are no widgets to display

Hello everyone
I’m using this beautiful plugin to display some custom menu widgets on a bunch of pages. That widget area is empty on a lot pages and I’d need to know where it’s empty for styling reasons.
I thought to add a class in my template to mark the pages in which the widget area is empty, I tried to set it like

<?php
if(!dynamic_sidebar('my-conditional-widgets'))
  $class = "has-no-widgets"; ?>
<div id="myDiv" class="myClass <?php echo $class; ?>">

however, it seems dynamic_sidebar() always returns true. I guess it might be because it’s not *really* empty, but turns out empty due to the plugin conditions.
Is there a better way to know if there are no widget to display?

Thank you in advance for any help.

https://www.ads-software.com/plugins/conditional-widgets/