Bootstrap grid while loop

Your while loop means, “Every time I have one post, output the following code.” Since you have 5 divs inside the while loop, you are getting 5 copies for each post. So, change your while { } code to this, which will output just 1 div for every post:

while($blogposts->have_posts()) {
    $blogposts->the_post(); ?>



<div class="col-md-6">
      <a href="https://wordpress.stackexchange.com/questions/359025/<?php the_permalink(); ?>
        <div class="card border-0">
          <div class="card-picture">

            <img class="card-img" src="<?php echo get_the_post_thumbnail_url(get_the_ID()); ?>" alt="Card image">

            <div class="card-img-overlay d-flex flex-column">
              <h5 class="card-title font-weight-bold"><?php the_title(); ?></h5>
              <div class="mt-auto"> Miika - <i class="fas fa-clock"></i> 16.2.2020 - Oppaat</div>
            </div>
          </div>
        </div>
      </a>
    </div>


    <?php }