/**
 * Use the Description from Global Setting, if the description is missing in the Post metabox
 */
add_action( 'rank_math/frontend/description', function( $description ) {
 global $post;
 $desc = RankMath\Post::get_meta( 'description', $post->ID );

 if ( is_product()) {
 $desc = RankMath\Helper::get_settings( "titles.pt_{$post->post_type}_description" );
 if ( $desc ) {
 return RankMath\Helper::replace_vars( $desc, $post );
 }
 }

 return $description;
});