drupal 9 view media entities standalone on own page

This is simply a configuration option that is disabled by deafult for some good reasons documented in the issue that removed the public display: Media items should not be available at /media/{id} to users with ‘view media’ permission by default [#3017935] | Drupal.org

Change in config/media.settings.yml that enables the media entity on its own page:

-standalone_url: false
+standalone_url: true

This module is not needed for there to be pretty paths, but rather is a fascinating way to change the paths of the files themselves, e.g. what you get if you view an image outside the context of the standalone media display page (or any other Drupal page)