Where to learn Javascript framework/library authoring? [closed]

Any search I try to make on this subject only yields results for learning existing JS frameworks. But I want to know what these guys know to write such frameworks themselves. When I checked out @headlessui/react for example, thinking it had simple enough components from which I can understand some basics of library development, I find they're still quite complex—the code structure, modular architecture, component organization and data flow... All that could be overwhelming. Very much different from what I would write if I were to create a simple, reusable component the best way I could think of!

I think it's more than just JavaScript design patterns I need to know. I'd like to write code and build things that people would use, but I find out there's still much I need to know. Can someone help me as to what resources/books can launch me in that direction? I've tried many times but never found what I was looking for. I already know and understand JavaScript so it makes me wonder where these guys are learning from.