it is all about the models and textures. there is no real magic thing you can do, it’s a combination of everything that makes it look great. unreal Paris is an arch viz, it has really high quality models and textures that use pbr, and it probably uses a tweaked light mass. post process can help a little to polish a scene, but if the models and textures are low quality it wont do much.
edit: also at that level of quality, you cant run it in real time. that’s just a matinee render.