Mysticism! After I updated one of my cameras with an old firmware 4.10.3.108, the other one that also worked with firmware 4.10.5.98 in motion detection mode! I am glad. It remains to try to upgrade the first camera to a modern firmware and look at the results.
I have a suspicion - when posting with support I provided a link to the post: Pan Cam (FW 4.10.5.34) No motion detection, tracking or notifications (12-30-2019) - #8 by g.paul.roy1
Maybe they fixed something in that direction? Who has cameras with the latest firmware - check if motion recognition has worked?