Enlarged image is LOWER resolution than the original

Actually I didn’t want to give any more advice when the right click is blocked. Why are you making it hard on the one who wants to help?

Anyway: for the lightbox image size there are some snippets depending on what is shown :

in your child-theme functions.php you can try this:

function avia_change_masonry_thumbnail_link($size){
  return "full";
}
add_filter('avf_avia_builder_masonry_lightbox_img_size', 'avia_change_masonry_thumbnail_link', 10, 1);

or that:

function avia_change_gallery_thumbnail_link($link, $attachment, $atts, $meta){
    $link = wp_get_attachment_image_src($attachment->ID, "full");
    return $link;
}
add_filter('avf_avia_builder_gallery_image_link', 'avia_change_gallery_thumbnail_link', 10, 4);

then the full image is taken instead of the large one!
if you like to enlarge the lightbox window – we will see when the above is done.