That’s sort of a myth

Cats and dogs will both eat their owner, but it’s not a given. Dogs are more likely to eat their owner, but cats will do it sooner.

https://www.science.org/content/article/yes-your-pet-might-eat-your-corpse-s-problem-investigators

Previous studies have revealed some differences between canine and feline scavenging. Dogs tend to eat the face and throats of humans, then break the ribs and chew on bones. Cats, on the other hand, often strip skin from the nose, upper lip, and fingers (the same places, Rando notes, that they nip at when playing with a living owner). Scavenging is more common with dogs than cats, Byard adds, “but I don’t trust either of them.”

Researchers think hunger is usually the main motivation, though some pets may not wait until their tummy starts to grumble. “Everyone wants to think it’d be a while,” Rando says. But animals might become worried about their unresponsive special person—especially if the death is violent or sudden—and lick their owner’s face seeking comfort. That licking can quickly turn into feeding.

…

If you’re worried about your pet eating you, Rando says, have someone regularly check on you—and your animals. “The commonality [in these pet scavenging cases] is that the person had been alone for a very long time.”