The old C++ FAQ book was over 500 pages, and that was decades ago. Those were the “frequent” questions.
I drove deep into C, a much simpler language, and there’s all kinds of wild stuff in there that most C devs don’t know. Of course, it’s not applicable to 99.9999% of C programming, so who practically cares, but to learn 100% of C++? I don’t have that kind of time.
That said, it’s totally possible to learn enough C++ that covers 99.9999% of its use cases.