sort CPT on Custom Taxonomy Archive page

I have created a custom post type called "al_product" and attached to it a custom taxonomy called "product_category".

In my archive-product_category.php I have this (relevant) code:

            if ( $  termchildren  ) {                 // we have kids...just show the terms.                            $  i=1;                 foreach ( $  termchildren as $  child ) {                     if ($  i % 2 == 0) {                         echo '<div class="tax-entry flex">';                     } else {                         echo '<div class="tax-entry flex" style="flex-direction: row-reverse;">';                     }                     ?>                         <figure class="wp-block-media-text__media">                             <?php if ( get_field('product_category_img', $  child) ) echo wp_get_attachment_image( get_field('product_category_img', $  child), 'full' ) ;?>                         </figure>                         <div style="flex:60% 0 0;" class="wp-block-media-text__content">                             <h2><?php echo $  child->name ;?></h2>                             <p>                                 <?php                                 if (get_field('short_description', $  child )){                                      echo get_field('short_description', $  child );                                 }else{                                     echo $  child->description;                                 }?>                             </p>                             <?php                             // Get (at most) 2 "product" posts in the child term.                             $  posts = get_posts( array(                                 'post_type'      => 'al_product',                                 'posts_per_page' => 2,                                 $  taxonomy_name   => $  child->slug,                             ) );                              // If there's exactly 1 post, use the post permalink.                             if ( 1 === count( $  posts ) ) : ?>                                 <a class="button" href="<?php the_permalink( $  posts[0] ); ?>">See this Product</a>                             <?php // Else, use the term link.                             else : ?>                                 <a class="button" href="<?php echo esc_url( get_term_link( $  child, $  taxonomy_name ) ); ?>">See this Series</a>                             <?php endif; ?>                          </div>                     </div> <!-- END FLEX -->                     <?php                     $  i++;                 }             } else {                  // no kids...show the products                 echo '<div class="productCategories grid">';                 while ( have_posts() ) : the_post();                     ?>                      <div class="product_cat">                         <a href="<?php the_permalink();?>">                             <?php the_post_thumbnail('small');?>                             <h2><?php the_title();?></h2>                             <?php                             $  subtitle = get_field('subtitle');                             if ( $  subtitle ) {                              echo '<h3 class="entry-subtitle">'.$  subtitle.'</h3>';                             }                             ?>                         </a>                         <?php //if (get_field('specs')['part_number']) echo '<span>'.get_field('specs')['part_number'].'</span>';?>                     </div>                  <?php                 endwhile;                 echo '</div>';             } 

The section I’m questioning is when there are no kids so we show products.

Currently this is returning the products correctly but sorting by title. I would like to sort by menu_order.

I added this to my functions.php:

add_action( 'pre_get_posts', 'rt_change_product_sort_order');  function rt_change_product_sort_order($  query){     if(get_query_var( 'product_category' )):        //Set the order ASC or DESC        $  query->set( 'order', 'DESC' );        //Set the orderby        $  query->set( 'orderby', 'menu_order' );     endif;     }; 

To no avail. I’ve also tried replacing the "If" statement with each of these:

if(is_post_type_archive( 'product_category' )): if(get_query_var( 'product_category' )): if(get_query_var( 'al_product' )): 

What am I missing here?