I don’t understand. Isn’t a magic, right? How it be possible? In real time? In Eevee, even enabling soft shadow makes the movement in viewport slow. If I see Lumen’s illumination in the video below not it draws realistic shadows from global illumination like 60fps.
Lumens GI solution uses a highly optimized software raytracer and other techniques. You can read up about it here: https://www.hardwaretimes.com/unreal-engine-5-lumen-vs-ray-tracing-whats-the-difference-and-which-one-is-better/