App has stopped opening on second monitor

Unfortunately, I went through all that when originally setting the system up, so all the boxes are unticked already. No idea why this has suddenly happened, as the set up has been working well for ages. No updates that I know of. The only thing that has happened was that I needed to unplug one montior while using Zoom the other day as, for the life of me, I can not get it to use the camera on the Mac and it prefers the camera on the second monitor (which then displays my filthy study for all to see). So I force the camera by unplugging the second monitor while using Zoom, which shoves everything temporarily onto the primary monitor. But I've done this numerous times before and everything always goes back where it belongs the next time I boot up. Except now. Everything seems to be running normally otherwise.

Unfortunately, no cigar. On either problem. I tried resetting the NVRAM. Is that all you do - hold down those keys until it boots? Should it look like it's booting any differently? Because while it booted a bit slower than normal, it appeared normal otherwise, so not sure I did it right. I also did startup in Safe Mode. Camera still on monitor 2 when I want it on 1. Email client still on monitor 1 when I want it on 2. Grrr.