How can I display the featured image in this shortcode pulling from ACF fields

I'm using the following shortcode which pulls from an ACF post object field and works to display post titles as links in a list:

function related_for_products( $atts ) {
global $post;
$related = get_field('product_related');
$html = '';
if( $related ) {
    $html .= '<ul>';
    foreach( $related as $option ) {
        $permalink = get_permalink( $option->ID );
        $title = get_the_title( $option->ID );
        $html .= '<li><a href="'. esc_url( $permalink ) . '">' . esc_html( $title ) . '</a></li>';
    }
    $html .= '</ul>';
}
return $html;
}
add_shortcode( 'related', 'related_for_products' );

How can I add the post featured image to the link element so both the title and the image display, and both link to the post? I've tried the following and variations but I must be getting my syntax wrong as I either get an empty image element or nothing at all.

function related_for_products( $atts ) {
global $post;
$related = get_field('product_related');
$html = '';
if( $related ) {
    $html .= '<ul>';
    foreach( $related as $option ) {
        $permalink = get_permalink( $option->ID );
        $title = get_the_title( $option->ID );
        $featured = get_the_post_thumbnail_url( $option->ID );
        $html .= '<li><a href="'. esc_url( $permalink ) . '">' . esc_html( $title ) . ' <img src="'. esc_url( $featured ) . '"></a></li>';
    }
    $html .= '</ul>';
 }
 return $html;
 }
 add_shortcode( 'related', 'related_for_products' );

You might try using

get_the_post_thumbnail($option->ID, "full")

instead. This will give you the full image with source set, etc.

it might look something like this:

$html .= '<li><a href="' . esc_url( $permalink ) . '"><h3>' . esc_html( $title ) . '</h3>' . $featured  . '</a></li>';

Maybe view the actual HTML that gets output (inspector or view-source) and you will be able to see why your image was empty.

lastly, (if you haven't already) use var_dump($featured); so you can see exactly what is being returned.