Just tried it on my Mac mini and it works fine with Bluetooth off. The specs do say it requires a MacBook Pro 2012 or newer
Buy Magic Trackpad 2 for Mac in Silver - Apple
but one would think that is just to get the required Bluetooth 4.0 and shouldn't matter when used wired.
"System Requirements Bluetooth 4.0-enabled Mac computer with OS X v10.11 or later".
High Sierra meets the OS X requirements.
I previously used my Trackpad 2 with a 2008 Mac Pro, which did not have Bluetooth 4.0. The automatic pairing by plugging in didn't work, but it would pair by turning the trackpad's power switch off then on. It also worked on that computer wired with Bluetooth off.
Are you plugged into a USB port on the computer, not via a hub? Do you have another Lightning cable to try?