strange issue with get_post_type() when using it in a shortcode in text widget

unfortunately I have no success with get_post_type() but get_queried_object() helped.

I changed the code to:

function post_type_slug()
{
    $post_type = get_queried_object();
    $post_type = $post_type->rewrite['slug'];

    return $post_type;
}
add_shortcode('pts', 'post_type_slug');

and it’s working in text widget now.