Comment from one of our trainers :-
It is very easy to end up with the lock screen in my Centos8 VM. It works like this: For some reason, VNC seems to think that the control or alt key is pressed; I hit a few keys and inadvertently hit the screen lock. At this point, I can only get back into the Desktop if I know the password. This happened to me right now; luckily (thanks to earlier bad experience) I had changed the password. Had I not done that, the only way to get back to the Desktop would be by rebooting it. So, a solution for people who bring up the screen lock would be great.