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.
Customer support service by UserEcho