Q My new Mac mini refused to recognise my wireless trackpad or mouse until fully set up. Is that normal?
A Pairing Bluetooth peripherals with a brand new Mac can be fiddly, as it depends on timing. It is usually simplest if you connect wired input devices at first, then once the system is configured, it is far easier to get those Bluetooth devices recognised by turning them off and on again.
It is also wise to keep a wired mouse and keyboard to hand in case of later problems. Because the driver to handle USB input devices is loaded earlier after startup, and it is less prone to system problems, you may be able to control your Mac with wired devices when wireless ones cannot function properly.
Updated from the original, which was first published in MacUser volume 30 issue 2, 2014.