new Mac mini can't connect the trackpad

Make sure the trackpad is turned on and charged.

Plug the trackpad into the mini to recharge it for 30 minutes or so if need be.

The trackpad can also be used while it is plugged into the mini.

Have you unpaired the trackpad from any previous Mac that may have been using it?

Connect an Apple wireless accessory with Mac - Apple Support:

https://support.apple.com/guide/mac-help/connect-an-apple-wireless-accessory-mchlp2656/mac