Is the standard documentation sufficient for an Android developer?

Question

Android

Suppose a developer has mastered all API Guides from Google ( https://developer.android.com/guide/index.html) and studied the accompanying Andriod APIs, understands and knows how to put all this into practice. How would you rate the level of his training? How big is the "secret" side of Android development, ie. what is the amount of knowledge that an Android professional needs, but is not included in the standard documentation? These can be both standard Android features, which for some reason were not included in Google guides, or must-have third-party libraries (for example, https://www.infinum.co/the-capsized-eight/articles...
We are talking about it is about knowledge, and not about the experience of the developer (it is clear that in the course of practical work, specific techniques are mastered that are not in any documentation).

Answer 1

Android development requires a certain set of standard third-party libraries. Why pile up your bikes, which are bound to have bugs?

Answer 2

You have gained knowledge of the Android API.
And now learn how to write good code from all this with a well-thought-out architecture, good OOP, tests, multithreading, etc.
At the very least, get used to building a UI using some kind of MV* pattern. You won't find it in Google guides, but you need it.
Also, as mentioned above, learn how to use the must have libraries. Not all of them are easy to use. Let's say you have to tinker with Dagger2 to understand how it works.