No pet door can guarantee a cat won’t go outside when the dog does.
The PlexiDor electronic door opens only for pets with a wireless receiver “key” on their collar, and a pet without a key can’t open the door. That doesn’t necessarily mean the cat can’t get outside. Cats are clever and quick and will figure out that they can run through the door once the dog has opened it.
Some cats dart through ahead of the dog, others run right behind it, and some brave felines go under the dog’s stomach.
Solving the problem will depend on more than the dog door. It might for instance be possible to use an indoor electronic cat fence to keep the cat away from the pet door.