How can i not show the_post_thumbnail if post is opened? - php

Question

I try to devolop my own wordpress theme. However i struggle with the following:
I added the loop to my content php and it is loaded by the page php
the template at the home site is the page.php.
the template when i click and load a post with its content is also the page.php
Ok. So now i have enabled thumbnails. But:
The Thumbnails also show up when i click and open the post.
I only want them to show up in the list of posts page, not in the posts itself.
How can i do that?
Please help me
index.php
<?php get_header(); ?>
<div id= "mainandcartwrapper" class="mainandcartwrapper">
<main>
<?php
$path = "C:\wamp64\www\almondo/wp-content/themes/almondotheme/";
$onlytemplate = str_replace($path,"", get_page_template());
echo $onlytemplate;
?>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
<?php get_template_part("template_parts/content"); ?>
<?php endwhile; else : ?>
<?php get_template_part("template_parts/content","error"); ?>
<?php endif; ?>
</main>
<?php get_sidebar(); ?>
</div>
<?php get_footer(); ?>
</div>
</body>
</html>
page.php
<?php get_header(); ?>
<div id= "mainandcartwrapper" class="mainandcartwrapper">
<main>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>
<?php
get_template_part("template_parts/content");
?>
<?php endwhile; else : ?>
<?php get_template_part("template_parts/content","error"); ?>
<?php endif; ?>
</main>
<?php get_sidebar(); ?>
</div>
<?php get_footer(); ?>
</div>
</body>
</html>
content.php
<article <?php post_class();?>>
<p class="text-l almondo-link">
<a href="<?php the_permalink();?>">
<?php the_title();
?>
<br>
<?php
$path = "C:\wamp64\www\almondo/wp-content/themes/almondotheme/";
$onlytemplate = str_replace($path,"", get_page_template());
echo $onlytemplate;
?>
<p>Veröffentlicht von <?php the_author(); ?> am <?php the_date("d.m.Y"); ?></p>
</a>
</p>
</article>
content_page.php
<article <?php post_class();?> >Statische Seite:
<p class="text-xs">
<?php the_title(); ?>
</p>
</article>
Have a nice Weekend,
Your Alwin