What popup? Do you mean the firewall? Unreal games always trigger the firewall, but you can just say no, the game does not need it.
They probably meant the promt to allow the installation of prerequisites through the Itch manager. Usually it's about getting some Redist, DX or Platform specific libraries (Here most likely the UEPrereq). Needs elevated rights too, so it's a good thing if people look twice there - but claiming it's a virus with no foundation is not.