Pagination functions won't work

Question

I have a custom post type named 'books' and in a static front page I display all the posts of this type. My problem is that I try to make pagination but all the functions that I found on the internet won't work. Here is my code and the functions like prev_next_posts_link() won't work. What am I doing wrong?

    $paged = ( get_query_var( 'page' ) ) ? get_query_var( 'page' ) : 1;
    $args = array(
        'post_type' => 'books',
        'posts_per_page' => 8,
        'paged' => $paged
    );
    $loop = new WP_Query( $args );?>

    while ( $loop->have_posts() ) : $loop->the_post();
            // some code
    endwhile; ?>


            <?php if ($loop->max_num_pages > 1) {  var_dump($loop->max_num_pages);?>

                <nav class="prev-next-posts">
                    <div class="prev-posts-link">
                        <?php echo get_next_posts_link( 'Older Entries', $loop->max_num_pages ); // display older posts link ?>
                    </div>
                    <div class="next-posts-link">
                        <?php echo get_previous_posts_link( 'Newer Entries' ); // display newer posts link ?>
                    </div>
                    <div>
                        <?php the_posts_pagination(array(
                                'mid_size' => 2,
                                'prev_text' => __( 'Back', 'textdomain' ),
                                'next_text' => __( 'Onward', 'textdomain' ),
                            )); ?>
                        </div>
                </nav>

Answer 1

Don't create a new query. You can use pre_get_posts for this type of works.

Example : If you want to add books and movies custom post type to home page main loop,

function books_movies_cpt_in_home($query) {
  if ($query->is_home() && $query->is_main_query()) {
    $query->set('post_type', array('books','movies'));
  }
}

add_action('pre_get_posts', 'books_movies_cpt_in_home');