Hi Kevin-
Thanks for reaching out and for using the Post and Page Builder for WordPress.
You’re right that the “Gallery” type blocks are different from the “Create Gallery” photo galleries, and it’s not super straightforward to make them open in the pop-up “lightbox” like the actual galleries do.
The easiest way to accomplish this is to add a standalone lightbox plugin, like Responsive Lightbox and Gallery. Make sure each image is using the Link To: Media file, and they’ll be automatically opened in a lightbox pop-up when that plugin is active.