Possums do not eat cats nor do the possums prey on cats.
However a possum may attack the cat and kill the cat if they are cornered by the cat or feel threatened by the cat.
Possums mostly eat things such as fruits, nuts, green plants, insects, snails, snakes, frogs, birds, and their eggs, as well as small mammals such as meadow voles, mice, and rats.
Possums are nocturnal omnivores and don't really want to eat cats or dogs or any other animals but like I mentioned before they will attack the cat or dog or other animal if they need too.
But your cat is usually safe around possums as long as the cat doesn't get near the possum.