Edited answer

Thank you for you clarification above, and please give this a try –

Note – This code assumes that you are using page.php, a variation of the page templage or some other custom template – it will not work on your index page (index.php).

<div id="page-<?php the_ID(); ?>">
<?php
if (have_posts()) : while (have_posts()) : the_post();

        if ( has_post_thumbnail() ) :
            the_post_thumbnail('thumbs');
        endif;
        
        
        echo get_the_date('jS F Y');
        
        the_title();
        
        the_content();
        
    endwhile;
endif;
?>
</div>

<?php
/** Query the list of posts to display */
$args = array(
    'post_type'     => 'post',
    'post_status'   => 'publish'
);
$posts_query = new WP_Query($args);
?>

<div id="post-list">
<?php
if($posts_query->have_posts()) : while ($posts_query->have_posts()) : $posts_query->the_post();
?>
        <div id="<?php the_ID(); ?>" <?php post_class(); ?>>
        
            <h1 class="post-title">
                <a href="<?php the_permalink(); ?>" title="View post '<?php the_title_attribute(); ?>'">
                    <?php the_title(); ?>
                </a>
            </h1>
            
            <p class="post-content">
                <?php echo substr(get_the_excerpt(), 0,200); ?>
            </p>
            
        </div>
<?php
    endwhile;

    wp_reset_postdata();

endif;
?>
</div>

Before/after the main Loop you have no need of the wp_reset_postdata() and wp_reset_query() fucntions at all.

However, after the secondary Loop to list the posts, just before the final endif; you’ll need just wp_reset_postdata().

You’ll see that I’ve added some HTML in the secondary Loop to give you an idea of how to do this – obviously you’ll need to do somehting similar to the primary Loop so that you can apply styling.