Thanks to Milo’s comment I could find a solution.
In my home.php I have deleted the custom query and inserted:
<div class="news-content col-12 col-xl-8">
<div class="row">
<h1>News</h1>
</div><!-- .row -->
<div class="row">
<?php
if ( have_posts() ) : while ( have_posts() ) : the_post();
if(has_post_thumbnail()) :?>
<div class="news-wrapper col-12 col-xl-6">
<div class="news-date">
<?php the_time('j.m.Y'); ?>
</div><!-- .news-date -->
<div class="news-img">
<?php the_post_thumbnail(); ?>
</div><!-- .news-img -->
<a class="news-title" href="https://wordpress.stackexchange.com/questions/304812/<?php the_permalink() ?>">
<?php the_title(); ?>
</a><!-- .news-title -->
<div class="news-text">
<?php echo short_excerpt(25); ?>
</div>
<a href="https://wordpress.stackexchange.com/questions/304812/<?php the_permalink() ?>" class="btn">
czytaj dalej
</a><!-- .btn -->
</div><!-- .news-wrapper -->
<?php else :?>
<div class="news-wrapper col-12 col-xl-6">
<div class="news-date">
<?php the_time('j.m.Y'); ?>
</div><!-- .news-date -->
<a class="news-title" href="https://wordpress.stackexchange.com/questions/304812/<?php the_permalink() ?>">
<?php the_title(); ?>
</a><!-- .news-title -->
<div class="news-text">
<?php echo short_news_content(70); ?>
</div>
<a href="https://wordpress.stackexchange.com/questions/304812/<?php the_permalink() ?>" class="btn">
czytaj dalej
</a><!-- .btn -->
</div><!-- .news-wrapper -->
<?php
endif;
endwhile;
endif;
?>
</div><!-- .row -->
<div class="row">
<?php the_posts_pagination( array( 'mid_size' => 2 ) ); ?>
</div>
</div><!-- .news-content -->
</div><!-- .container -->
</div><!-- .main-content -->
and in my functions.php file I have added:
add_action( 'pre_get_posts', 'custom_post_on_homepage' );
function custom_post_on_homepage( $query ) {
if ( is_home() && $query->is_main_query() )
{
$query->set('post_type', 'news');
$query->set( 'posts_per_page', '4' );
}
}
Hope this helps someone in the future.