https://farscape.fandom.com/wiki/Inter-dimensional_entity
The IdE is a common Sci-Fi trope, but how would anyone know if they could be real? Unless a person has seen one, or is an intrepid researcher, they wouldn't know.
https://en.wikipedia.org/wiki/Interdimensional_UFO_hypothesis
https://now.northropgrumman.com/do-doors-to-interdimensional-travel-exist
https://en.wikipedia.org/wiki/Interdimensional_UFO_hypothesis#John_Keel_and_'Ultraterrestrials'