ECS is a one of the possible designs of what we usually call "the gamestate" that is the dynamic structure that holds the game world simulation.

But the origin of ECS is Data Oriented Design, also known as DOD, that emerged as a reaction to the bad properties of OOP.

DOD is more general and IMHO more interesting than ECS.

I have not yet seen a satisfying implementation of ECS, it can be extremely fast compared to OOP approach, but also cumbersome when dealing with dependencies between systems and the ways to handle structural changes.

My take would be : learn the principles, do some benchmark, but do not consider any ECS implementation as gospel, this is not mature yet.

Use the ideas and principles to build a fast simulation in your own way.