In order for a YouTube link to embed here on AB it must:
(a) have a space, or a carriage return, at either end of it, so that AB's server can pick it up among all the other text on a page ;
(b) include the 'https' bit at the start ;
(c) be in the form 'youtube.com', and not in the 'youtu.be' format used by mobile devices ; and
(d) include 'watch?v=', followed by the video's unique number, in the link.
Links that have 'shorts', instead of 'watch' in them, won't work.