Mail App Not working
The Mail app opens, but the window does not appear. You could see the banner across the top. But you cannot see your mail because the actual window is missing.
MacBook Pro 15″, macOS 11.1
Question marked as
Hours later with technical support we stumbled across a very simple solution. Hold down the shift key and select the Mail app. Boom! You might have to do that a couple of times for it to reset.