Lightbox popup on Enfold

replace in your code:

$(window).load(function() {
// with:
$(window).on('load', function(){

so that there is then:

function inline_popup_enabler(){
?>
<script>
(function($){
  $(window).on('load',function(){
    $('.inline_popup').magnificPopup({
      type:'inline',
      midClick: true
    });
  });
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'inline_popup_enabler');

i’m participant as you are – so if there is a private content link – i can not see.
but you can try:

.mfp-inline-holder .mfp-content, 
.mfp-ajax-holder .mfp-content {
  width: 80vw;
}

first try this filter in your child-theme functions.php :

add_filter( 'avf_default_lightbox_no_scroll', '__return_true' );

if it does not work –

you can give in your case to that text manuall the second custom class: no-scroll
Just put to that place where you entered your inline-popup class
so enter : inline-popup no-scroll

_____________
Why do I mention : “in your case”.
Mostly you can’t assign the trigger class directly to the link. e.g. a button ALB – the custom class would go to a parent element of the link ( so it’s not at the anchor).
So I mostly enter the trigger class to a parent element – and noted this inline popup snippet like this way:

function inline_popup_enabler(){
?>
<script>
(function($){
  $(window).on('load',function(){
    $('.inline-popup').find('a').addClass('no-scroll');
    $('.inline_popup').magnificPopup({
      delegate: 'a',
      type:'inline',
      midClick: true
    });
  });
})(jQuery);
</script>
<?php
}
add_action('wp_footer', 'inline_popup_enabler');

But now since Enfold 5.1 there is this filter: avf_default_lightbox_no_scroll

by the way – you can set the submenu :

on Content Tab “Sticky Submenu” to stick to the header when it scrolls down. ;)

your script is working – but i would play a bit with your colors to get a better usability:

#top #wrap_all .av-subnav-menu > li.current-menu-item a {
  text-decoration: none !important;
}
#top #wrap_all .av-subnav-menu > li.current-menu-item a > .avia-menu-text {
  background-color: #678908;
  border-color: #678908;
}