Show only last WooCommerce category products in related section

If you want to only show products from the last category inside your WooCommerce related products section, then place the code below into your functions.php.

add_filter( 'woocommerce_get_related_product_cat_terms', 'last_child_cats_only', 10, 2 );
function last_child_cats_only( $term_ids, $product ) {
	
	if(!$product) {
		return $term_ids;
	}

    $cats_array = array();
    $terms = wp_get_post_terms($product, 'product_cat');
    foreach ( $terms as $key => $term ){
        $check_for_children = get_categories(array('parent' => $term->term_id, 'taxonomy' => 'product_cat'));
        if(empty($check_for_children)){
            $cats_array[] = $term->term_id;
        }
    }

    if(!empty($cats_array)) {
    	$term_ids = $cats_array;
    }

   	return $term_ids;

}