Today I realized that when I start up my iMac (Big Sur 11.1) It usually takes longer than usual to load the startup applications and there is a suspicious element that is an empty window called "Window" then it disappears as quickly from the Dock as the element itself, which is a quarter-space screen, so fast that I can't get a screenshot to show you. I have tried disabling all the initial apps one by one, and still this item keeps popping up. Anyone know if this is normal? A Big Sur anomaly perhaps? Thank you and I would appreciate your help to solve this problem.