Firstly, I resort to crediting an intelligent agent as a possible cause based on what intelligent agents have demonstrated they can do - generate information.
It is no more necessary that the origin of the intelligent agent be known to accept it as a possibility than to accept the big bang when we have no idea how it came about either. Or accept evolution as the theory of how life changes and species arise when we do not know how the first life/species arose.
5+ billion years does not mean much without a credible mechanism.