Study the React source code and implement your own mini-version. It's a great way to deepen framework specific knowledge (if that's what you are after) and also learning more about the language used to create the framework.

Start with these articles:

https://medium.com/react-in-depth/inside-fiber-in-depth-over...

https://medium.com/dailyjs/the-how-and-why-on-reacts-usage-o...

https://github.com/acdlite/react-fiber-architecture

https://www.youtube.com/watch?v=ZCuYPiUIONs

https://github.com/facebook/react/issues/7942#issue-18237349...