Why is there still voltage in my wires when the breaker is off?
What you are seeing is called phantom voltage.
This is a voltage induced from another live circuit that is running parallel to your now dead circuit.
Proof the breaker worked all the lights went out.
Phantom voltage is a voltage and depending on several factors it may be 120v but there is no current potential thus the lights are out.
There is a possibility that this could be part of a multiwire branch circuit
And the neutral is conducting the other circuits power back to the source.
And that’s why multiwire branch circuits require handle ties by modern code.