Mac Setup
I have turned on the Mac keyboard and wireless mouse but the Mac mini is prompting to go to support.apple/macsetup but cannot get them to work.
Mac mini 2018 or later
If they are the older wireless keyboard and mouse with replaceable batteries, dig out, borrow, buy an inexpensive USB keyboard and mouse to get setup and pare your wireless devices.
If they are the new rechargeable wireless keyboard and mouse, connect them to the Mac mini using the supplied charging cable to get setup.