Get link for taxonomy to show top-level terms

@Webelaine already answered your question.

You’re working against yourself – just create a custom post type called product.

Note that custom post types can be hierarchial (like pages), if that’s what you’re after.

EDIT

Taking into consideration what the OP stated in the comments area, the best advice that I can offer is “create a custom page template” where you query all of the top level taxonomy terms.

The code for that would be:

$args = [
  'taxonomy'     => 'product_category',
  'parent'        => 0,
  'hide_empty'    => false           
];
$terms = get_terms( $args );
// loop through all terms
foreach( $terms as $term ) {
  // display only the term name
  echo '<h4>' . $term->name . '</h4>';
}

Hope that helps