Here I am not talking about Beaver Builder module’s toggle field option. Value of 2nd drop down field of BB module will generate via WP AJAX action. Currently I am cooking another cool module for Beaver builder and this kind of functionality is required there. So I am sharing my experience for my pro members.
Right now I am giving the simple example here. Assuming that you are building the custom module and will fetch the post titles list based on post type value. So 1st drop down will contain the all post types and 2nd drop down will show the all titles based on post type value.