WP posts on external page…*with thumbnails*

Hello, I am trying to get the latest WP posts onto a non-WP page within the site. I have been using this method (as recommended elswhere in this forum) https://www.jamischarles.com/blog/get-wp-posts-without-hacking/

However, this method only includes the Post Title and Permalink. I was able to modify the above script to also include an excerpt of the post below the title and link. However, I also want to include the post thumbnail so that I can display an image next to the link and excerpt. I have tried many many things but somehow I am unable to make this work. There doesn’t seem to be an obvious way to call the thumbnail like there is the title ($post_title).

The page in question is here: https://www.christmas-cookies.com/wptest.php

function displayHomePosts(){
	//default values obj from post.php.
	//pass these in as args that you really want
	$defaults = array(
    		'numberposts' => 5, 'offset' => 0,
    		'category' => 0, 'orderby' => 'post_date',
    		'order' => 'DESC', 'include' => '',
    		'exclude' => '', 'meta_key' => '',
    		'meta_value' =>'', 'post_type' => 'post',
    		'suppress_filters' => true
	);

	$args = array(
    		'numberposts' => 4
	);

	//explore why the redirect error occurs?
	//$num = 5;
	$post_array = get_posts($args  ); //as found in wp-includes/post.php
	//var_dump($post_array); 

	//add the last className for the bottom border?
	echo "<ul>";

	for($i=0; $i<count($post_array); $i++){
		$post_title = $post_array[$i]->post_title;
		$shortpost_title = substr($post_title, 0, strpos($post_title, ' ', 10));
		$post_name = $post_array[$i]->post_name;
		$post_content = $post_array[$i]->post_content;
		$post_blurb = substr($post_content, 0, strpos($post_content, ' ', 200));
		$post_permalink = "https://www.christmas-cookies.com/blog/" . $post_name;

                //actually output the html with the php variables included
		echo "<li><b><a href=\"$post_permalink\" rel=\"bookmark\" title=\"Permanent Link to $post_title\">$post_title</a></b><br />$post_blurb...  <a href=\"$post_permalink\">Read <b>$shortpost_title >></b></a></li>";
	}
	echo "</ul>";

}

Can someone please tell me how to add the thumbnail? THANK YOU!