For what I read in Level streaming for infinite space in multiplayer - Epic Games Forums this isn’t properly solved in UE4, I don’t have a degree in computer science but I want to try solving this problem, what should I study to make this work?
Those posts are over 7 years old. Unreal has changed a bit since then. 
I would say that this problem has been solved from a technical point-of-view. It’s more of a design problem now.
For huge (or even infinite) levels, you need to use Level Streaming, so only part of the level is being generated at any one time, otherwise it would crash (what with the level using infinite resources ).
You also need to use Procedural Generation, so you can generate the level section based on it’s unique place in the world, so you don’t have to save the details once you have generated it. The idea is to be able generate the bit of the world from the least amount of data possible.
This video on Procedural Generation using Blueprints from the official Unreal Engine channel is quite old, but the fundamentals still hold true.
Finally, for a less technical, more design-orientated take on ProcGen, try this essay from Kate Compton, concerning her famous "10,000 bowls of oatmeal" problem.