The controls for Side Car are now located in the "Screen" section of the new Control Center. It does seem a bit fragmented because the display settings control is still available without it. But see attached screenshot. - https://www.icloud.com/iclouddrive/0CuCQOzloKZpYq_xWLYB2QS0Q#Screen_Shot_2020-09-17_at_9.04.19_PM