Looks like they changed up some things in the lemmy-ansible repository, resulting in the docker guide being outdated.
Take a look at this nginx config file instead: https://github.com/LemmyNet/lemmy-ansible/blob/main/templates/nginx_internal.conf It splits incoming requests and directs them to either the UI server or the backend server.
Copy the link from the federation-link-hexagon-thing button and paste it into the search bar on your instance. The post should get fetched, and should show up as a result.