Spacious Theme – thumbnail based archive page

My goal is to have a thumbnail-based archive page which shows only the thumbnail and the post title in a grid on a separate archive page.

I am working on the spacious theme and already set up a child theme. Spacious already has a built-in archive.php but I couldnt chose it as template in the dashboard therefore I created a new file called archive-page.php in the child folder shich is an exact copy of the archive.php file and which I can adjust with the following code in it:

<?php
/*
Template Name: page-archive
*/
?>

<?php get_header(); ?>

<?php do_action( ‘spacious_before_body_content’ ); ?>

<div id=”primary”>
<div id=”content” class=”clearfix”>

<?php if ( have_posts() ) : ?>

<?php while ( have_posts() ) : the_post(); ?>

<?php if ( has_post_thumbnail()) : ?> ” title=”<?php
the_title_attribute(); ?>” >
<?php the_post_thumbnail(thumbnail, array(‘class’ => ‘alignleft’)); ?>

<?php endif; ?>

<?php get_template_part( ‘content’, get_post_format() ); ?>

<?php endwhile; ?>

<?php get_template_part( ‘navigation’, ‘archive’ ); ?>

<?php else : ?>

<?php get_template_part( ‘no-results’, ‘archive’ ); ?>

<?php endif; ?>

</div><!– #content –>
</div><!– #primary –>

<?php spacious_sidebar_select(); ?>

<?php do_action( ‘spacious_after_body_content’ ); ?>

<?php get_footer(); ?>

Now I can chose the archive template in the page section of the dashboard but of course it does not show the archive in the way I want it. Can someone help me with how I have to adapt the code (php) to make appear the thumbnails?

I would be very thankful for every help available (also links to tutorials or code snippets…)!
Thank you!