I was reading through Thunder’s issues and here one of the devs of lemmy says that youtube/peertube embed links are already supported in the backend with post.embed_video_url.
I’m not sure how easy would be to implement that embed in the different apps/lemmyUI however!
I was confused as well and I found this coloured version and this version with sea connections (green for Panama and Suez canal) that helped me to understand!