I’m doing a test for the way the front end editor works when not logged in to this site. I am not logged in!
But to reference the technical request I am trying to sort out, here is a test of some links which should be supported by WordPress auto embeds.
(Note added: This is what it looked like when composing)
Try YouTube?
(Just a plain link here, no embed preview)
Try Flickr?
(Just a plain link here, no embed preview)
Try Giphy?
(not even official listed as supporting but it works everywhere I try)
(Just a plain link here, no embed preview)