lightbox issues

the enfold is working with anchors as icons and the corresponding href.

but you can have your own lightbox script for those pages – using the magnificPopup :

function mixed_media_lightbox() {
?>
<script type="text/javascript">
window.addEventListener("DOMContentLoaded", function () { 
(function($){
    $('.widget_media_image').magnificPopup({
      delegate: 'img',
      type: 'image',
      removalDelay: 500,  // to allow animated closing in ms
      mainClass: 'avia-popup mfp-zoom-in mfp-image-loaded mixed-media',  
      midClick: true,
      gallery: { enabled:true },
        image: {
          titleSrc: false,
          markup: '<div class="mfp-figure">'+
                    '<div class="mfp-close"></div>'+
                    '<div class="mfp-img"></div>'+
                      '<div class="mfp-bottom-bar">'+
                        '<div class="mfp-title"></div>'+
                      '</div>'+
                  '</div>',
        
          },  
      callbacks: {
        elementParse: function(item) {
          item.src = item.el.attr('src').replace( /-\d*x\d*\./, '.' );
        },
        markupParse: function (template, values, item) {
          if ( item.el.closest('.panel-grid-cell').find('.widget_text').length ) {
            values.title = '<h3 class="heading">' + item.el.closest('.panel-grid-cell').find('.widget_text').html() + '</h3>';
          } else {
            values.title = '<h3 class="heading">' + item.el.find('img').attr('title') + '</h3>';
          }
        },
      },
    });

})(jQuery);
});
</script>
<?php
}
add_action('wp_footer', 'mixed_media_lightbox', 9999);

your img tags have no title nor alt attributes – but we can use the following description.

Now – what you have to do. : not all your images do have that widget_text
See Paintings Page. Or you have tried to do it with enfold lightbox implementation there. ?

the script is working – but the shown title is not allways defined. the reason – see above.

Best would be to set an alt or title tag as fallback to all of your images. For SEO purpose it might be better to use the alt tag.
then you had to change the else condition to:

values.title = '<h3 class="heading">' + item.el.find('img').attr('alt') + '</h3>';