Remove post type slug of all post types from permalinks

 function gp_remove_cpt_slug( $post_link, $post ) {
        if ( 'race' === $post->post_type && 'publish' === $post->post_status ) {
            $post_link = str_replace( "https://wordpress.stackexchange.com/" . $post->post_type . "https://wordpress.stackexchange.com/", "https://wordpress.stackexchange.com/", $post_link );
        }
        return $post_link;
    }
    add_filter( 'post_type_link', 'gp_remove_cpt_slug', 10, 2 );

At this point, trying to view the link would result in a 404 (Page Not Found) error. That’s because WordPress only knows that Posts and Pages can have URLs like domain.com/post-name/ or domain.com/page-name/. We need to teach it that our custom post type’s posts can also have URLs like domain.com/cpt-post-name/.

<?php
/**
 * Have WordPress match postname to any of our public post types (post, page, race).
 * All of our public post types can have /post-name/ as the slug, so they need to be unique across all posts.
 * By default, WordPress only accounts for posts and pages where the slug is /post-name/.
 *
 * @param $query The current query.
 */
function gp_add_cpt_post_names_to_main_query( $query ) {
    // Bail if this is not the main query.
    if ( ! $query->is_main_query() ) {
        return;
    }
    // Bail if this query doesn't match our very specific rewrite rule.
    if ( ! isset( $query->query['page'] ) || 2 !== count( $query->query ) ) {
        return;
    }
    // Bail if we're not querying based on the post name.
    if ( empty( $query->query['name'] ) ) {
        return;
    }
    // Add CPT to the list of post types WP will include when it queries based on the post name.
    $query->set( 'post_type', array( 'post', 'page', 'race' ) );
}
add_action( 'pre_get_posts', 'gp_add_cpt_post_names_to_main_query' );

That’s it! Just change both instances of race in these code samples to the slug of your custom post type, and replace gp_ with whatever function prefix you’d like (your initials would be fine), and you should be all set. Going to Settings > Permalinks and saving the permalink structure to end in /%postname%/ may also be necessary.