After upgrading to 2021.2.1: When you use direct view URL, it does not prompt for authentication.
Temporary workaround is:
Option 1: Login to https://tableau.admin.uillinois.edu and try URL again.
Option2: Add /#/signin?redirect= parameter in URL after the server name and it will prompt for login.
Example: https://tableau.admin.uillinois.edu/#/signin?redirect=views/BoxyBoxBox/LandingPage?:showAppBanner=false&:display_count=n&:showVizHome=n&:origin=viz_share_link