Can’t connect mouse and keyboard to the imac

Hello, jmkoval.

Have you unpaired your devices from any Mac or device they might have been paired with previously?

Connect a wireless accessory with Mac - Apple Support:

https://support.apple.com/guide/mac-help/connect-apple-wireless-keyboard-mouse-mchlp2656/10.13/mac/10.13

Set up your Magic Keyboard, Magic Mouse or Magic Trackpad - Apple Support:

https://support.apple.com/en-us/HT201178

If you can't connect your Magic Keyboard, Magic Mouse... - Apple Support:

https://support.apple.com/en-us/HT204621