Beginner question: Can I make massive maps?

Well I am completely new to Game Development, I started recently and I am having fun with it. I’m not expecting to get where I want to be any time soon, but I do wonder what the limit is.
I wanted to know how creating truly massive open world maps would work, I get that there are limits, but how do certain games like No Mans’s Sky and Star Citizen achieve that?
Is that even possible in Unreal Engine 5 and if so how would that even work?

Thank you to anyone who can answer this.