Show posts with and without meta_key and order them the ones with meta_key on the top

posts-metakey.php

<?php

   $args = array(
       'post_type' => 'projects',
       'posts_per_page' => 9,
       'post_status' => 'publish',
       'meta_query' => array(
           'relation' => 'OR',
           array(
               'key' => 'featured-checkbox',
               'value' => 'yes',
               'compare' => 'EXISTS'
           ),
           array(
               'key' => 'featured-checkbox',
               'compare' => 'NOT EXISTS'
           )
       ),
       'orderby' => 'meta_value_num title',
       'order' => 'ASC',
   );
 
 
     $featured = new WP_Query($args);

     if ($featured->have_posts()): while($featured->have_posts()): $featured->the_post(); ?>
             <div class="c-image"><?php the_post_thumbnail('large'); ?></div>
             <div class="cstext">
                        <article>
                             <h2><?php the_title(); ?></h2>
                             <?php the_content(); ?>
                             <a href="<?php echo get_permalink(); ?>" class="readmore">Learn More</a>
                     </article>

             </div>

     <?php
             endwhile;
                     else: 'No Content Added';
     endif; ?>