WordPress / Disable duplicate content for categories

functions.php

<?php
/**
 * Disable duplicate content for categories.
 *
 * @author Guy Dumais.
 * @link https://en.guydumais.digital/how-to-avoid-duplicate-content-in-wordpress/
 */
add_action( 'wp_head', $af = function() {

    // Add noindex, follow robot meta tag for categories.
    if ( is_category() ) {
        wp_no_robots();
    }

} );
unset( $af );