Nav Menu, Search | Type: PHPAdd search form to specific nav menu

add_filter('wp_nav_menu_items', 'add_search_form', 10, 2);
 
 function add_search_form($items, $args) {
          if( $args->theme_location == 'MENU-NAME' )
          $items .= '<li class="search"><form role="search" method="get" id="searchform" action="'.home_url( '/' ).'"><input type="text" value="search" name="s" id="s" /><input type="submit" id="searchsubmit" value="'. esc_attr__('Search') .'" /></form></li>';
     return $items;
}

Reference Links

https://wpdynamic.com/wordpress-developer/wordpress-code-snippets/how-to-add-a-wordpress-search-form-to-a-specific-wp_nav_menu/