My iMac will not connect to my mouse or keyboard

Have a look at > If you can't connect your Magic Keyboard, Magic Mouse, or Magic Trackpad to your Mac - Apple Support

If you have the Rechargeable Magic Keyboard and Mouse.

Connect your Keyboard to your Mac with the Lightning to USB Charging Cable.

Connect your Mouse to you Mac with the USB-C to Lightning Cable for 1 minute, then disconnect the cable from the mouse.

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