The Arduino IDE is a good starting point to code with the Gamebuino, but it lacks features that one can expect from a modern development environment:
VSCode is an open source IDE from Microsoft (more or less based on Visual Studio) that provides all these modern features under the name IntelliSense and supports Arduino development. So it is normal to try to use it with the Gamebuino.
There is already a tutorial in french by delay for the basic steps, and a forum post by Crystal Noir regarding the proper configuration of "IntelliSense" (the VSCode set of functions for context-aware features). This is a good basis, but I could not really make IntelliSense work as expected, with unpredictable results. Eventually, by chance, it worked.
So I found the problem deserves more in-depth analysis, and a decent understanding of the "obscure reasons". So here we are! Consider this tutorial as the English version of the other one, with some formalization of the IntelliSense configuration.
Please go to the full tutorial on GitHub.
As soon as the MarkDown editor is available for the Gamebuino pages, I will copy the content of the tutorial here.