You'd want to read more than one book. And in my opinion you also need to digest the C++ Core guidelines and also use something like clang-tidy with high sensitivity, and when issues are flagged go dig into the details.

But then you realize it's just all too much, and you're looking for something less complex again.

I wonder how useful a C++ that I could understand in its entirety would be. But I don't understand english in its entirety either. I use what I know and get by just fine.