The effect consists of a Niagara system for the edges of the portal (the beam and the steam/clouds it emits), as well as a plane with a material that I've built using noise textures and triangular masks. I also modified the default post-process lens flares and added a dirt mask. Inspired by the portal in Man of Steel (General Zod's Trial scene). Background is good ol' SM_Rock, meshes in corners are Sci-fi Props by Qwestgamp (https://skfb.ly/6WMuC) licensed under CC BY 4.0