BOINC 7.16.11 Screen Saver (in a Lenovo-AIO-730S running Windows 10 v 20H2 Build 19042.1288) Doesn't ...
1. ... allow the screen to go dark (hibernate), making it the opposite of a screen saver. Until very recently, the screen would be dark while World Community Grid was running in background; now, BOINC loads a screen showing WCG status and that screen remains displayed until user input (from the keyboard or mouse) is sensed.

2. ... always allow user control of the machine without restarting the machine. On one occasion today, moving the mouse caused BOINC to clear the screen "saver" and display a white screen. I had to do a power-down reset to get control of my machine.