Every person with a companion animal should do their own research, but I’ve known a few people who have switched their dogs and/or cats to an all plant-based diet. I remember one anecdote about a dog’s digestive problems going away after the switch. And in the case of cats it can be hit or miss - there’s something about the cats ph levels that need to be kept track of. Some cats respond to these diets positively, while others don’t. So sometimes cats are obligate carnivores, and others not so much. There’s still a lot to learn.