Create Custom Page Taxonomy

create-custom-page-toxonomy.php

// Create Page Category Custom Taxonomy (page post type)

function register_page_category_taxonomy() {
    register_taxonomy('page_category', 'page', [
        'label'        => 'Page Categories',
        'public'       => true,
        'hierarchical' => true,
        'show_ui'      => true,
        'show_admin_column' => true,
    ]);
}
add_action('init', 'register_page_category_taxonomy');


// Add Filter Dropdown to Admin List Table (page post type)

function add_page_category_filter_to_admin() {
    global $typenow;

    if ($typenow === 'page') {
        $taxonomy = 'page_category';
        $taxonomy_obj = get_taxonomy($taxonomy);
        $terms = get_terms([
            'taxonomy' => $taxonomy,
            'hide_empty' => false,
        ]);

        if (!empty($terms)) {
            echo '<select name="' . esc_attr($taxonomy) . '" class="postform">';
            echo '<option value="">' . esc_html($taxonomy_obj->labels->all_items) . '</option>';
            foreach ($terms as $term) {
                $selected = (!empty($_GET[$taxonomy]) && $_GET[$taxonomy] == $term->slug) ? ' selected="selected"' : '';
                echo '<option value="' . esc_attr($term->slug) . '"' . $selected . '>' . esc_html($term->name) . '</option>';
            }
            echo '</select>';
        }
    }
}
add_action('restrict_manage_posts', 'add_page_category_filter_to_admin');


// Modify the Query to Filter by Selected Term

function filter_pages_by_page_category($query) {
    global $pagenow;
    
    if ($pagenow === 'edit.php' && isset($_GET['post_type']) && $_GET['post_type'] === 'page' && isset($_GET['page_category']) && $_GET['page_category'] !== '') {
        $query->query_vars['tax_query'] = [[
            'taxonomy' => 'page_category',
            'field'    => 'slug',
            'terms'    => $_GET['page_category'],
        ]];
    }
}
add_filter('pre_get_posts', 'filter_pages_by_page_category');