For custom popup trigger, shortcode of the form is required in the post/page to build the required prototype of the popup. If you add trigger using WordPress default editors (Classic/Gutenberg), it’s automatically get added in the page/post and remain hidden.
But for other editors where editors do not have eForm shorcode generator, required shortcode get missing. Hence you need to add following code which is required for triggering the popup properly along with the custom link having class eform-manual-popup and proper href set to #ipt-fsqm-popup-form-{id} .
You would need replace only the form id in the following code and you need to put this code any where in the page/post.
<!-- wp:eformv4/popup-form {"form_id":"{id}","pos":"h"} /-->