I recently installed the beta on my S21 (Google Fi) and haven't been able to interact with the top of my screen near the status bar. This does not occur in Settings, but persists on all other apps. This leads me to think that it might be an app overlaying on top of the UI since no apps should be able to overlay Settings. What troubles me is that this did not occur before I installed the beta, so it could possibly be a compatibility issue with some apps that do have overlays.
I turned off some of the offending apps to find it now works. The apps in question are Energy Ring and Access Dots.
Just a warning for those of you who might use these apps with the new One UI.