The link does not work.

What I see is a mishmash of information.

Is there a better resource you can recommend?

Such a long article without a single illustrative example.

So now you could rewrite it for the gba with very high level libraries like for exemple Butano in C++ (no assembly, no registers) : https://gbadev.net/getting-started.html#high-level-developme...

It doesn't even show an example of a json file and its equivalent in muon.