Steps:
1. Add a Layout Block to your page
2. Add an Image Block inside the layout for each image in your gallery
3. For every image block, go to its settings and under 'On Tap' enable "Open image in lightbox"
4. Save & Publish
That's it. When a member taps any image, it opens in the lightbox and prev/next arrows appear so they can navigate through all the images in the layout block without closing it.
Note: Only images with Open in Lightbox enabled will appear in the lightbox gallery. When a member taps one of these images, it opens full-screen with left/right arrows to navigate between all lightbox-enabled images on that page.