I need help with lag reduction

You know how big games like ark: survival evolved, and Fortnite have good graphics, well in my game I can barely use one decent model and my computer frames drop.

how do big games do this? And could I do it?

Im not an expert, but if you want to get good performance, your models should have low poly-counts. Details can be added through Normal maps. I’m sorry if this didn’t help.