FixedUpdate has nothing to do with VSync. This is why there’s interpolation on rigidbodies to update per-frame in-between the fixed frame-rates of physics.
Time.deltaTime is the per-frame time, not the per fixed-update time which is Time.fixedDeltaTime. The exception to this is in the docs where Time.deltaTime returns the fixed delta-time when read from within the FixedUpdate callback.
Note: Here’s how to post code . 