Add the "missing" `item_class`, `item_link_class` and `current_item_link_class` arguments to `wp_nav_menu`.

filters.php

<?php

/**
 * Adds support for passing `item_class` to `wp_nav_menu`.
 */
add_filter('nav_menu_css_class', function ($class_names, $item, $args) {
    if (property_exists($args, 'item_class')) {
        return array_merge($class_names, explode(' ', $args->item_class));
    }

    return $class_names;
}, 10, 3);

/**
 * Adds support for passing `item_link_class` and `current_item_link_class` to
 * `wp_nav_menu`.
 */
add_filter('nav_menu_link_attributes', function ($atts, $item, $args, $depth) {
    $classes = array();
    if (property_exists($args, 'item_link_class')) {
        array_push($classes, $args->item_link_class);
    }

    if (property_exists($args, 'current_item_link_class')
        && in_array('current-menu-item', $item->classes)) {
        array_push($classes, $args->current_item_link_class);
    }

    if (!empty($classes)) {
        $atts['class'] = implode(' ', $classes);
    }

    return $atts;
}, 10, 4);