Add Search Toggle at End of Menu

change-search-form.php

<?php //<~ don't add me in

add_filter( 'get_search_form', 'wpb_alter_search_form', 20 );
	// Modify Search Form
	function wpb_alter_search_form( $form ){
	    return '<form role="search" method="get" id="searchform" action="' . esc_url( home_url( '/' ) ) . '" >
	    <input type="search"  name="s"  placeholder="SEARCH..." value/>
	    </form>';
}

menu-location.php

<?php //<~ don't add me in

add_filter('wp_nav_menu_primary-menu_items', 'wpb_add_search_toggle', 10, 2);
// Filter in Search Toggle to end of primary menu
function wpb_add_search_toggle($items, $args) {
        $items .= '<li class="search search-wpb"><a class="search-icon"><i class="fas fa-search"></i></a><div style="display:none;" class="wpbsearchform">'. get_search_form(false) .'</div></li>';
        return $items;
}

search.css

/********************
 * Search Navigation
 ********************/

.search-wpb .fa-search {
    color: #666666;
    font-weight: 900;
}

.search-wpb .fa-search:hover, 
.search-wpb .fa-search:focus {
    color: #999999;
    text-decoration: none;
}

.wpbsearchform{
    display: block;
    width: 400px;
    position: absolute;
    right: 0;
    top: 100%;
    margin-top: 1px;
    z-index: 9999;
    background-color: rgba(200,199,197,0.8);
    padding: 0;
    border-radius: 0;
     -webkit-box-shadow: 0 1px 10px rgba(0,0,0,0.15);
    box-shadow: 0 1px 10px rgba(0,0,0,0.15);
    border: 1px solid #ccc;
}

.wpbsearchform form input:focus {
    color: #555;
}

.wpbsearchform input[type="search"] {
	border-radius: 0;
}

.wpbsearchform ::-moz-placeholder {
	color: #999 !important;
	font-weight: 300;
	opacity: 1;
}

.wpbsearchform ::-webkit-input-placeholder {
	color: #999 !important;
	font-weight: 300;
}

search.js

jQuery(document).ready(function($){
	
	/* Search Menu */
	
	$(".search-icon").click(function() {
		$(".wpbsearchform").slideToggle();
	});

	$(document).keyup(function(e) {
		// Ref https://stackoverflow.com/questions/3369593/how-to-detect-escape-key-press-with-pure-js-or-jquery
		// Close search if esc key pressed
		if (e.key == "Escape") {
		  $(".wpbsearchform").hide();
		}
	});

});

themelocation.php

<?php //<~ don't add me in

add_filter('wp_nav_menu_items', 'wpb_add_search_toggle', 10, 2);
// Filter in Search Toggle to end of primary menu
function wpb_add_search_toggle($items, $args) {
    if( $args->theme_location == 'header' ) //Swap to your location
        $items .= '<li class="search search-wpb"><a class="search-icon"><i class="fas fa-search"></i></a><div style="display:none;" class="wpbsearchform">'. get_search_form(false) .'</div></li>';
        return $items;
}

Hello. Thank you for your example. What which do you have the searchform?