URL Rewriting in WordPress for only one specific page

Let’s start by getting rid of the rules you’ve added to your .htaccess. This is WPSE and the page is running inside of WordPress, so we’re going to rely on WP to do the rewriting.

You’re going to want to register CD_Produit as a query variable so WordPress’ front controller is aware of it.

function wpse427745_add_query_vars($vars) {
  $vars[] = 'CD_Produit'; 
  return $vars;
}


add_filter('query_vars', 'wpse427745_add_query_vars');

Next you need to add the rewrite:

function wpse427745_add_rewrite_rule($rules) {
  $new_rules = array('CD_Produit/([^/]+)/?$' => 'index.php?pagename=products&CD_Produit=$matches[1]');
  $rules = $new_rules + $rules;
  return $rules;
}
 
add_filter('rewrite_rules_array', 'wpse427745_add_rewrite_rules');

Visit Settings > Permalinks and hit “Save Changes” (which refreshes all permalinks, not just the ones listed on the Settings page) and you should be good to go.