The URL link for the a YouTube Short is at https://www.youtube.com/shorts/linkshortcode

Per @JustinRatliff, just replace /shorts/ with /watch?v=

So that format is....

www.youtube.com/watch?v=linkshortcode

The link for the YouTube Short vide of mine is at https://www.youtube.com/shorts/-nCgaiEDpp8.

Therefore, the correct link to input for posting is https://www.youtube.com/watch?v=-nCgaiEDpp8.

Insert using the YouTube video button in BBCODE...