Some things to consider: descriptions will have to be retrieved via either the YouTube or Invidious APIs, the privacy-enchanced embedded player uses a different domain (https://www.youtube-nocookie.com/), embeds happen on the https://www.youtube.com/embed/video_id format. Also, I don't think there is an element with ID "movie_player" in the embedded page.
Currently, annotations don't work on embedded YouTube videos.
I have done some work towards this support, but I haven't been able to get far: https://github.com/tech234a/AnnotationsRestored/commit/a630dfb95dd48e6e43fad353baa62f2043b30fd2.
Some things to consider: descriptions will have to be retrieved via either the YouTube or Invidious APIs, the privacy-enchanced embedded player uses a different domain (https://www.youtube-nocookie.com/), embeds happen on the https://www.youtube.com/embed/video_id format. Also, I don't think there is an element with ID "movie_player" in the embedded page.