Does Magic Trackpad 2 work with Mac without Bluetooth?
Does Magic Trackpad 2 works with Mac without Bluetooth?


Yes.


  Is it possible to connect it through the USB to Lightning cable, to a computer that doesn't have Bluetooth?


Yes.


  Or does the cable work just for charging, and the communication is Bluetooth-only?


The communication can be done over cable, just like how a wired keyboard or a Trackpad would work.

This Apple Support document sheds more light:


https://support.apple.com/guide/mac-help/mchlp2656/mac



  Connect a Magic Keyboard, Magic Mouse 2 or Magic Trackpad 2 with your Mac
  
  When you connect your keyboard, mouse or trackpad to your Mac, it automatically connects with the Mac using Bluetooth.
  
  
  Connect one end of a Lightning to USB Cable to your Magic Keyboard, Magic Mouse 2 or Magic Trackpad 2 and the other end to the USB port on your Mac. Depending on your Mac, you may need an adapter, which is available from an Apple Store or on apple.com.
  
  
  You can use your Magic Keyboard or Magic Trackpad 2 while it’s connected to your Mac. You can’t use your Magic Mouse 2 while it’s connected.


A Magic Mouse can't be used as the Lighting port is located at the bottom of the mouse making it impractical to use it with the cable connected.

Quoted text added for context. Emphasis on the italicised part.