VSCode C++ on Mac shows Intellisense code completions slowly and without documentation

I'm using VSCode for C++ programming on Mac OS for the first time. I am very carefully going through the online tutorial Using Clang in Visual Studio Code.

I am using:

• VSCode 1.59.1
• clang Apple LLVM version 8.0.0 (clang-800.0.42.1)
• MacBook Air 2017 with Mac OS Sierra (10.12). Yes, I know it's old.

At one point in the tutorial, the authors talk about the IntelliSense code completion:

Start typing msg. as you would when calling a member function. You should immediately see a completion list that shows all the member functions, and a window that shows the type information for the msg object.

They show this screenshot with function call documentation:

However, when I create the exact same code add try to retrieve the code completion, I encounter two problems:

1. The code completion pops up fairly slowly, at least a full second after I type msg..
2. There is no documentation on the function call.

What is wrong? Do I just need a newer MacBook?