my php code works and it doesn't

I am upgrading an old WP page. and a part of it is to introduce widgets.
Some of my previous code I want to present in your widget in order to simplify possible changes in a child-theme.

I have this piece of code:

<?php $args = array(
	'posts_per_page'  => 20,
	'offset'          => 0,
	'category'        => 11,
	'orderby'         => 'post_date',
	'order'           => 'DESC',
	'include'         => '',
	'exclude'         => '',
	'meta_key'        => '',
	'meta_value'      => '',
	'post_type'       => 'post',
	'post_mime_type'  => '',
	'post_parent'     => '',
	'post_status'     => 'publish',
	'suppress_filters' => true );

$postslist = get_posts( $args );
foreach ($postslist as $post) :  setup_postdata($post); ?>
	<div>
		<a href="<?php the_permalink(); ?>"><?php if ( has_post_thumbnail() ) { the_post_thumbnail(thumbnail); } ?>
	</br>
		<?php the_title(); ?></a>
	</br></br>
	</div>
<?php endforeach; ?>

it is working in my old theme, showing 20 posts thumbs and headlines. I am using it to present my category “photo album” in sidebar.

the code is working, when it is hard-coded into sidebar.php, but when it is placed in your widget plugin – it doesn’t (it just shows the same post 20-times)

What is wrong?

https://www.ads-software.com/plugins/php-code-widget/