I've just tested my iPad Pro 11 with iPadOS13.4.1. I was able to save several bookmarks to my Home screen in the fashion that has always been done. Next I tested several pages from YouTube. I would say this is not a bug, but an intentional change in what YouTube allows you to save. I also tried saving the same pages as bookmarks. All of them worked as bookmarks. Like I said earlier, I believe this is something that YouTube has done, since they spend the early part of your visit trying to get you to download their app to use, and will not allow all features to be used in Safari. I would address your question to YouTube.