Add search field in nav menu WP

add-search-in-nav.php

/**
  * Add search field in nav menu WP.
  * @author Everaldo Matias <matiaseveraldo@gmail.com>
  * @link https://developer.wordpress.org/reference/functions/get_search_form/ 
  */

add_filter( 'wp_nav_menu_items', 'add_search_in_nav' );
function add_search_in_nav() {
    // If this isn't the responsive-menu, do nothing.
    if ( ! ( $args->theme_location == 'responsive-menu' ) )
    return $items;

    // Otherwise, add search form in initial nav.
    return '<li class="search-in-nav">' . get_search_form( false ) . '</li>' . $items;
}