Display posts with tag for custom post type only
get_the_tags() is a shortcut function to get the terms from the post_tags taxonomy. What you have done is make a new and different taxonomy. And you will need to use get_the_terms() to get your required data. E.g. $terms = get_the_terms($post, ‘image-gallery_tags’); https://developer.wordpress.org/reference/functions/get_the_terms/