The recordable window option doesn't really work for me, it just flickers trying to draw over the overlay (i think it doesn't disable the overlay while its active? so its duplicating it). It also seems to break with the screen buffer option set to at least 1 frame, and starts copying the window bar at the top downward until it fills the whole screen
The recordable window is intended to be used only by your recording software. Once you created the recordable window (move it a bit out the way), open your recording software and start recording the recordable window. You can now click on the button Hide the window so it doesn't bother you.
If you want to know why it's like this : if the overlay was recordable, the boxes would flicker as the bodies would be detected then hidden by the overlay the next frame. So Hotscreen has to be "invisible" by screen recording softwares and create a duplicated recordable window when necessary.