The recent photo obviously has "stand-in" wheels - I'd bet those came from some other vehicle - so maybe the production line for the correct wheels is no up and running yet - or maybe what we saw in the older photo were clip-on "aero-wheels". The tires probably have the wrong tread-pattern too...
I don't think Rivian turn all four wheels inwards like in your diagram. Adding true four-wheel steering with independent direction on each wheel would be crazy-complicated. I think it does exactly what a "skid steer" Bobcat does - keep all the wheels parallel - but put the wheels on one side...
I think there is some confusion here. All you get with rear-wheel steering is the ability to turn the rear wheels in the same direction as the front (the "crab walk") - or in the opposite direction, which gets you a tighter turning circle - but not much else.
TANK TURN: A "Tank Turn" doesn't...