There is vegan cat food which is complete and healthy. Fortified with the essential vitamines and things like taurine and completely safe. They also add this to meat based cat food - there really is no difference except that one doesn’t require dead animals, so there doesn’t have to be a contradiction to begin with and cats can be vegan.

That being said, hypothetically, let’s say it was a necessity. I happen to have carnivore pets myself whose food does not have a vegan variant so I get this question quite a lot.

Vegans will have pets for one of two reasons: either they already had the pet before they went vegan, or they rescued it. (Buying pets is not vegan, so if a supposed vegan does this, they’re full of shit)

In the first case, they are the animals carer and the animal relies on them so it’s their job to feed them. Giving the animal up would make no sense. We’re trying to do the best we can for the animal, and we can’t just release pets, and putting them in a shelter would not be beneficial.

In the second case, rescuing animals is vegan as fuck. When you do, you take on the responsibility of caring for the animal. Because you didn’t buy them, you are not increasing demand. Had the pet had a different carer, they’d still be eating that food so you’re not increasing that demand either. You’re just fulfilling your responsibility.