Embedding a YouTube Short video is not the same as embedding a regular YouTube video. The procedure for a Short is a little different.
The most important part of a YouTube short video is the video ID. For instance, this is the URL for a short video.
https://youtube.com/shorts/hZykPRVe4Ag?feature=shareThis is the part you need: hZykPRVe4Ag
Embed it in this format.
It will post the video like this:
[video:youtube]
[video]
There may be another way, but this way works.