What is the difference in the output methods?

Question

WordPress

Hello!
What is the difference in output?
Like this:

<?php
  global $wp_query;

  $wp_query = new WP_Query(array(
    'category_name' => 'blog', // 
    'posts_per_page' => '5',
    'paged' => get_query_var('paged') ?: 1 // страница пагинации
  ));

while(have_posts()) { the_post(); ?>
      <div><?php the_title(); ?></div>
<?php }

the_posts_pagination(); 

wp_reset_query(); // сброс $wp_query
?>

And this:

<?php 
    $query_projects = new WP_Query(array( 
      'category_name' => 'blog', 
           'posts_per_page' => 5
      ));
    ?>

       <?php while( $query_projects->have_posts() ): $query_projects->the_post(); ?>
                            <div><?php the_title(); ?></div>
             <?php endwhile; the_posts_pagination(); wp_reset_postdata(); ?>

Both use WP_Query and fetch blog posts. But in the first case, the output is through: while(have_posts()) { the_post();, and in the second

while( $query_projects->have_posts() ): $query_projects->the_post();

, while the first option allows you to display pagination through the_posts_pagination(); , but the second one is not.
What is the difference between these two options?