That law is not yet in effect. It will go into effect in 2025. However, we're already in the transition, meaning that small used dealers might still be using paper plates. Most of the larger dealers are already licensing cars before sales (a cost you were always required to pay--it's just that now the dealer pays it and then you pay the dealer than a separate check to the county tax assessor-collector's office).

Most of the smaller used car lots will generally just keep the plates that had been on the vehicle previously. If you want to sell a car whose license plate is of some specialized type rather than the standard serialized plate, the person who is selling the car must relicense. I have a specialized plate, so if I sold my car, I have to relicense it first.