Include account creation / log in after form submit

Hi,

You can use the hook rwmb_frontend_after_process to check the user if not logged in then update the post status to draft and redirect to the login page.

Here is the sample code

add_action( 'rwmb_frontend_after_process', function( $config, $post_id ) {
    if( ! is_user_logged_in() ) {
        // Update post
        $my_post = array(
          'ID'           => $post_id,
          'post_status'   => 'draft',
        );

        // Update the post into the database
        wp_update_post( $my_post );

        // Redirect to the page
        wp_redirect( home_url() );
        die();
    }
}, 99, 2 );

For more information, please follow the documentation
https://docs.metabox.io/extensions/mb-frontend-submission/#form-actions
https://developer.wordpress.org/reference/functions/is_user_logged_in/
https://developer.wordpress.org/reference/functions/wp_update_post/