Many startup shortcuts unavailable in Mojave 10.14.6?

The first sign of trouble was the Stall. The system would freeze, the Wacom cursor would freeze, then, after a few minutes, it would unfreeze, and all the attempts I had made to move during the Stall would happen in a second. The mouse cursor was moveable, but not usable. A helpful source in the forums said other users had had trouble with the latest Mac OS upgrade mixing with Screen Saver. That turned out to be the case with my system. It would run fine until I simply touched the Screen Saver pref tab. Stall would follow. In order to diagnose the problem I tried restarting in Safe mode. Couldnt do it, so I backed up a step further to zapping the PRAM. Couldnt do that either. So has Apple abandoned all its startup options, or am I the victim of some screwup in the OS upgrade, or both? The computer functions all right, but how will I know when its going to Stall again, and how do I adjust my screen saver choices?