I just imported a project into 2021.1.4f1. I noticed a new component in my imported character and clicked on the small icon on the top right in the Inspector. All I got was a missing page. The component is the new Skeleton Asset added by the 2D Animation package. It's probably documented in the package specific documentation but clicking on the icon on the top right doesn't redirect to that page. I've noticed that many times already but never bothered posting about it. Today is a different day; I'm not in the accommodating mood, sorry.