/**
 * Creating a new (custm) block category.
 *
 * @param   array $categories     List of block categories.
 * @return  array
 */
function wpdocs_new_block_category( $categories ) {
    // Plugin’s block category title and slug.
    $block_category = array( 'title' => esc_html__( 'My Plugin', 'text-domain' ), 'slug' => 'myplugin' );
    $category_slugs = wp_list_pluck( $categories, 'slug' );

    if ( ! in_array( $block_category['slug'], $category_slugs, true ) ) {
        $categories = array_merge(
            $categories,
            array(
                array(
                    'title' => $block_category['title'], // Required
                    'slug'  => $block_category['slug'], // Required
                    'icon'  => 'wordpress', // Slug of a WordPress Dashicon or custom SVG
                ),
            )
        );
    }

    return $categories;
}
add_filter( 'block_categories', 'wpdocs_new_block_category' );