There's no error message, I could not post the video link when I clicked on the video button or tried to paste the link into the text field. I tried both Chrome and Safari (I have a Mac). I could see nothing in the browser console (fyi: I do use some ad blockers, maybe that has something to do with it, since the review window pops up when I want to edit it).
The "edit" menu option in the browser lit up when I tried to paste but nothing happened. It seems to be the general paste option (I also tried it with pure text). Copy & Paste in notepad works, so it seems to be an itch.io-thing. Weirdly, pasting in forum posts and comments works fine, so this seems to be limited to the review section. Again, maybe it's something with the pop-up of the review-edit?
Fyi: I have the same bug when trying to write a review (not just edit it), I just tried. I did not have the same problem before and have last successfully reviewed a game a few days ago, so if it is a bug, it might be more recent).
Thank you!