I'm running the latest TeamViewer 15.12.4 on macOS Big Sur, with two monitors, one 3840x2160 and one 1920x1080. The management popover on a hosting machine cannot be used if the "Hide" button is clicked. It will effectively jam itself into the top left corner of the rightmost monitor, and completely hide the "Show" button from the leftmost monitor, making it impossible to remedy the effect of hiding the window. So I have to leave it visible on my main monitor at all times.
