22.04 doesn't detect external monitors

I've just upgraded to 22.04 from 20.04. Lenovo E560 i7 laptop with external monitor. The monitor is not detected. I've tried other monitors, but all the Displays program shows is "Unknown Default" monitor. "Detect Monitors" does nothing.

If I boot up on the built-in LCD, then plug in the external one, the display is duplicated on the external monitor, the mouse transfers to the external, and the LCD remains frozen.

Any ideas?