UE 5 requires so high specs even 5090 can't meet. It's a turd of an engine.

Nanite is a way to make cheaper but lower performance assets (yes, it performs worse than manual Level Of Detail optimizations and quite significantly).

Lumen requirements are so high that for it to perform good you basically have to render at 720p. So they do and then upscale, and it's all blurry and still runs like shit.