It's not really a dark pattern when the Acrylic plate is the product that most people are trying to buy - without it you don't have the physical numberplate you can put on your car.
Plus they make it pretty clear what the tickbox is, on top of the fact that an upsell of £20 for a physically made product on top of £30k for a license is the least useful upsell in the history of selling.
It's labeled "Uncheck this box if you DO NOT require a set of Acrylic Number Plates" and comes pre-checked.