All matter and energy exists in the universe, as the universe consists of everything that exists.
So outside of the universe cannot exist, because there is no matter or energy. And if something isn't made of matter or energy it cannot exist.
(And as a side note if a religious person says god exists outside of the universe they have just described them out of existence

Even a point in space and time exists. So outside of space and time does not exist.
Does this make sense to anyone? I'm probably completely wrong, but I'm just trying to make sense of what's outside of the universe.