If you look at the parts placement picture of the Teensy 4.0 on the PJRC web page, you can actually see which vias are connected to the USB port before the Vanished in the multilayer PCB.
Problem than is the very tiny size of the vias and you have to have a very small soldering tip to be able to connect a wire to those vias.
It can be done but is tricky. the two vias are those right of the Q1 letters.