/**
 * High-performance category gallery setup
 * Limits posts, avoids expensive loops, works with gridsby gallery template
 */
add_action( 'pre_get_posts', function( $query ) {

    // Only modify main query on front-end category pages
    if ( $query->is_main_query() && !is_admin() && $query->is_category() ) {

        // 1. Limit number of posts per category
        $num = intval( get_theme_mod('gridsby_category_num_posts') );
        if ( !$num || $num < 1 ) $num = 12; // default 12
        $query->set( 'posts_per_page', $num );

        // 2. Disable expensive WordPress features for speed
        $query->set('no_found_rows', true);         // disables COUNT(*) for pagination
        $query->set('update_post_meta_cache', false);
        $query->set('update_post_term_cache', false);

        // 3. Optional: only load 'image' post formats for gallery view
        $query->set( 'tax_query', array(
            array(
                'taxonomy' => 'post_format',
                'field' => 'slug',
                'terms' => array('post-format-image'),
                'operator' => 'IN',
            ),
        ) );
    }
});

/**
 * Choose gallery template efficiently
 */
add_filter( 'template_include', function( $template ) {

    if ( is_category() || is_tag() ) {

        // Lightweight check: does category contain only 'image' posts?
        $image_only = ! ( new WP_Query(array(
            'cat' => get_queried_object_id(),
            'posts_per_page' => 1,
            'post_type' => 'post',
            'post_status' => 'publish',
            'tax_query' => array(
                array(
                    'taxonomy' => 'post_format',
                    'field' => 'slug',
                    'terms' => array('post-format-image'),
                    'operator' => 'NOT IN',
                )
            )
        )) )->have_posts();

        if ( $image_only ) {
            $template = get_query_template( 'archive-image' );
        }
    }

    return $template;
});

/**
 * Load gallery scripts/styles for category pages efficiently
 */
add_action( 'wp_enqueue_scripts', function() {

    if ( is_category() || is_tag() ) {

        // Only enqueue scripts if gallery view is active
        $image_only = ! ( new WP_Query(array(
            'cat' => get_queried_object_id(),
            'posts_per_page' => 1,
            'post_type' => 'post',
            'post_status' => 'publish',
            'tax_query' => array(
                array(
                    'taxonomy' => 'post_format',
                    'field' => 'slug',
                    'terms' => array('post-format-image'),
                    'operator' => 'NOT IN',
                )
            )
        )) )->have_posts();

        if ( $image_only ) {
            wp_enqueue_style( 'gridsby-grid-css', get_template_directory_uri() . '/css/grid.css' ); 
            wp_enqueue_script( 'gridsby-grid3d', get_template_directory_uri() . '/js/grid3d.js', array(), false, true ); 
            wp_enqueue_script( 'gridsby-masonry', get_template_directory_uri() . '/js/masonry.pkgd.js', array(), false, true );
            wp_enqueue_script( 'gridsby-gridsby-gallery', get_template_directory_uri() . '/js/gridsby-gallery.js', array(), false, true );
        }
    }
});

<h1>Error thrown</h1><p>Call to undefined function html_tag_schema()</p>