Add row after three columns

on my newssite i have the first post in a full-width column, after that all older post are in three columns per row. But now i want that wordpress put after every three columns a and to keeps the elements into rows. I tried to adjust the following solutions: Solution 1 Solution 2 Solution 3

But nothing of that will work.

Here is my code to get my posts:

       <div id="primary" class="content-area">
    <main id="main" class="site-main" role="main">
   <div class=" entry-content">
   <?php if (have_posts()) : ?>
   <?php $post = $posts[0]; $c=0;?>
   <?php while (have_posts()) : the_post(); ?>

   <?php $c++;
   if( !$paged && $c == 1) :?>

        <?php get_template_part( 'template-parts/content', 'aktuelles-first' ); ?>

   <div class="accordion">
   <div class="row">

   <?php else :?>
    <?php get_template_part( 'template-parts/content', 'aktuelles' ); ?>


      <?php endif;?>

   <?php endwhile; ?>

   <?php endif; ?>

       </div></div>

    </main><!-- #main -->
       </div><!-- #primary -->

Is there any solution without changing my way to get the posts?

via Chebli Mohamed