Remove CPT permalink base

<?php

/**
 * Use only for specific CPT posts
 */
define('PM_CPT_NAME', 'courses');

/**
 * The function that detects the CPT posts permalinks
 */
function pm_detect_cpt_slugs($query) {
    global $wpdb, $pm_query, $wp, $wp_rewrite;

    // Do not run when Elementor is opened
    if((!empty($_REQUEST['action']) && strpos($_REQUEST['action'], 'elementor') !== false) || isset($_REQUEST['elementor-preview'])) {
        return $query;
    }

    // 1. Get the slug
    preg_match("/([^\/]+)(?:\/{$wp_rewrite->pagination_base}\/([\d]+))?$/", $wp->request, $parts);

    if(!empty($parts[1])) {
        $post_name = basename($parts[1]);
        $post_type = PM_CPT_NAME;

        // 2. Check if the slug is assigned to any post item
        $sql_query = "SELECT ID FROM $wpdb->posts WHERE 1=1 AND post_name = %s AND post_type = %s";
        $post_id = $wpdb->get_var($wpdb->prepare($sql_query, array($post_name, $post_type)));

        // 3. Filter the query if post was found
        if(!empty($post_id)) {
            $post = get_post($post_id);

            if(empty($post->post_type)) { return $query; }

            $post_type_object = get_post_type_object($post->post_type);
            $final_uri = (!empty($post->post_name)) ? $post->post_name : false;

            // Fix for hierarchical CPT & pages
            if(!(empty($post->ancestors)) && !empty($post_type_object->hierarchical)) {
                foreach($post->ancestors as $parent) {
                    $parent = get_post($parent);

                    if($parent && $parent->post_name) {
                        $final_uri = $parent->post_name . '/' . $final_uri;
                    }
                }
            }

            $new_query = array(
                'post_type' => $post->post_type,
                $post->post_type => $final_uri,
                'name' => $final_uri,
                'do_not_redirect' => 1,
            );

            // 4. Disable canonical redirect
            remove_action('template_redirect', 'wp_old_slug_redirect');
            remove_action('template_redirect', 'redirect_canonical');
            add_filter('wpml_is_redirected', '__return_false', 99, 2);
            add_filter('pll_check_canonical_url', '__return_false', 99, 2);

            $query = $new_query;
        }
    }

    if(isset($_GET['debug_query'])) {
        echo sprintf('<pre>Old query: %s</pre>', print_r($query, true));
        echo (!empty($new_query)) ? sprintf('<pre>New query: %s</pre>', print_r($new_query, true)) : '';
        echo (!empty($parts)) ? sprintf('<pre>Parts: %s</pre>', print_r($parts, true)) : '';
        die();
    }

    return $query;
}
add_filter('request', 'pm_detect_cpt_slugs', 9999);

function bis_filter_cpt_permalinks($url, $element) {
    if(!empty($element->post_type) && ($element->post_type == PM_CPT_NAME)) {
        $full_uri = get_page_uri($element->ID);
        $url = trim(get_option('home'), '/') . "/{$full_uri}";
    }

    return $url;
}
add_filter('post_type_link', 'bis_filter_cpt_permalinks', 999, 2);

function pm_redirect_native_cpt_permalinks() {
    global $wp;

    if(!empty($wp->request) && is_singular(PM_CPT_NAME)) {
        $cpt_data = get_post_type_object(PM_CPT_NAME);
        $cpt_slug = preg_quote($cpt_data->rewrite['slug'], '/');

        if(!empty($cpt_slug) && preg_match("/^({$cpt_slug})/", $wp->request)) {
            $url = get_permalink();
            wp_safe_redirect($url, 301);
            exit();
        }
    }
}
add_action('template_redirect', 'pm_redirect_native_cpt_permalinks', 1);