Dequeue BB Magnific Popup not working

Hi, I followed the instructions given in this post to disable magnificpopup.js/.css:

But the code snippet
add_filter( 'fl_builder_override_lightbox', '__return_true' );
does not change anything. The magnificpopup.js is still there.
Right now the only way to disable the BB Lightbox was with the setting “deactivate other lightbox scripts” in FooBox.
Is there a way to deactivate BB Lightbox? Should the code above work? I disabled other plugins but coudn’t get rid of the script.
It is deactivated in customizer and the add_filter line is added to my functions.php in my child theme.
Thanks for any help.