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I noticed something similar yesterday when upgrading a customer remotely.  She had been on 10.13.6 and was connected to my ScreenConnect with the Support client.  After the upgrade I could only see the menu bar and a blank desktop.  Ended up using a different product to finish with her.

Today I set up a new 10.15.4 VM and tested. On the first go round I ended up with the same result, menu bar only.  I had checkmarked the program in Accessibility.  Don't recall seeing any prompt about granting access for screen recording.  When I tried again I did get a prompt for screen recording.  When I enabled that it worked fine.