New iMac

Only to recharge the batteries. See the following from the "In the Box" section of iMac - Technical Specifications - Apple

iMac or

iMac with Retina 4K display

Magic Keyboard

Magic Mouse 2

Power cord

Lightning to USB Cable

Polishing cloth

For details on the Magic Keyboard and Magic Mouse 2, see: Magic Keyboard - US English - Apple and https://www.apple.com/shop/product/MLA02LL/A/magic-mouse-2-silver

I apologize if this seems too obvious ,but as many other posters here appear unaccustomed to keyboards and mice having power switches, I have to ask, did you find the switches?