loop – Prevent Duplicate Post Counted by Query

<?php 
while ( have_posts() ) : the_post(); 
    
    $get_series_id = get_post_meta( get_the_ID(), 'series_seri', true );
    
    if (in_array($get_series_id, $do_not_duplicate)) {
            continue; // We've already seen this post ID, so skip the rest of the loop
        }
    
$do_not_duplicate() = $get_series_id;
?>
<?php the_title(); ?>
<?php endwhile; wp_reset_postdata(); ?>

how to make duplicate post not counted ? i wanna show 20 post, but in frontpage only showing 5 post because duplicate post also counted,