I hope I don't get too confused posting this...
I've noticed that youtube shorts don't embed properly.
If I use the normal way they come out like this
[youtube]https://www.youtube.com/shorts/U7C5-E9q4j8[/youtube]
The url is
https://www.youtube.com/shorts/U7C5-E9q4j8
BUT, if you take out the shorts/ bit and replace with watch?v= to make
https://www.youtube.com/watch?v=U7C5-E9q4j8 it will embed properly.
[youtube]https://www.youtube.com/watch?v=U7C5-E9q4j8[/youtube]
At least it does sometimes. It seems to have not worked, unless I remove the first one. It's confusing...