Starting with Catalina Developer Beta 5, third-party screensavers are no longer able to receive and respond to keyboard and mouse events. Many third-party screensavers make use of this feature. The new behavior is clearly wrong - documentation for ScreenSaverView says that it is a NSView subclass, and thus we should be able to override keyboard and mouse events.
Submitted as FB6916019
I'll guess they will not change it. This will be the default behavior.
Would be great to see a new API for screen savers at anytime in the future.