WP Post Query with variable item column size

<?php

$args = array(
    'posts_per_page' => 10,
    'post_type' => 'post',
);

$query = new WP_Query( $args );

?>

<?php if( $query->have_posts() ) : ?>
<div class='post_wrapper row'>
    <?php $count = 1;?>
    <?php while ( $query->have_posts() ) : $query->the_post(); ?>
    <?php 
        
        if($count===1){
            $col_class ='col-12';
         }else{
            $col_class ='col-6';
         }?>

    <div class="<?php echo $col_class?>">
        <a href="<?php the_permalink(); ?>"><?php the_title(); ?></a>
    </div>

    <?php $count++;?>
    <?php endwhile; ?>
</div>
<?php endif; ?>

<?php wp_reset_query(); ?>