From my experience, and what I see a number of people struggling with is the overarching concepts of React. I've yet to find a good tutorial or video that covers the theory of how React is meant to work. It's a sticking point that takes a long time to click for people not coming from a conceptually similar library.
What I mean is the stuff that comes long before the Hello World example, like what a component actually is, and why one would want to split their project into components. How and why ES6 classes, imports, etc., are used the way they are in React. How React's life cycle, state, etc., play into deciding how to break down a thing into components.
It's the theory that is missing. Like in high school auto shop where before you ever touch an engine, they explain the physics of how small explosions are converted into rotational motion, if that analogy makes sense.
Ronald Roe
Developer