Clarified has the Colorbox lightbox feature for viewing images. When you use the WordPress Gallery Shortcode (even the block gallery), you will get a popup lightbox.
NOTE: We are planning to remove the lightbox in the next update because it does not work with actual image captions correctly (not compatible). We will be offering an alternative.
- Go to Appearance > Customize > Other Options
- Look for the Enable Gallery Lightbox setting and toggle the setting
- Click the Publish button
Option: The recommended and alternative is to check out a free plugin called WP Featherlight. This works with the classic editor and the block editor galleries. Of course, you also have the option to use other gallery plugins if you need something more robust.