It has often been the case that the external displays go to sleep and the cursor moves off the laptop screen as if going on the external monitor but the screen is black and no cursor appears. I have always resolved that by turning the external display off and back on.

I have run Catalina for several years with two external monitors that I "located" using the Displays tab in System Preferences and then choosing "Arrangement." I just downloaded (upgraded?) to Big Sur and the "Arrangement" tab no longer appears. Anyone help?