Comment 2 for bug 1963986

I can confirm the following will fix this issue.

htdocs/export/html/lib.php
Line 65:
       private $scripts = array('jquery', 'popper.min', 'bootstrap.min', 'dock', 'modal', 'lodash', 'gridstack', 'gridlayout', 'masonry.min', 'select2.full', 'fancybox.min', 'theme');

Line 1085:
Add fancybox file to export
$directoriestocopy[get_config('docroot') . 'js/fancybox/jquery.fancybox.min.js'] = $jsdir . 'fancybox.min.js';

Also:
Copy jquery.fancybox.min.css to /htdocs/theme/raw/style/jquery.fancybox.min.css (original location is js/fancybox/jquery.fancybox.min.css)