In older themes, we were using a third-party ColorBox lightbox script that uses the image “title” for captions and not the actual image caption. This created many problems if you wanted to use the real caption.
If you would like a lightbox for your website and the Prologe theme, we recommend checking out the WP Featherlight plugin. Currently, it works for the WP Gallery shortcode and also the Block Images/Galleries. We are using it on the live demo for this theme and for the Rough Pixels website.