I’ve heard that.
Carl Sagan also said the distances are just far too great which I also agree with.
The fourth dimension is the dimension of time.
If the distances are too great and the fourth dimension is time I have also heard that perhaps these UFOs are traveling in the 4th dimension.
If they travel in time not in distance in the fourth dimension. I’m thinking they’re either advanced civilization from Earth’s past or they are earths future.
Manifestations of the Devil? Well, there’s that.