It’s hard to understand what the actual question here is. If it’s an issue with IntelliJ not indexing your project, put a screenshot of how that looks like. Are you using IntelliJ or Android Studio as the guide explicitly says? Impossible to tell from your description.
Beyond that, what kind of code are you planning to contribute? Something to core Compose? Something to Jetbrains’s version of it? Something to IntelliJ itself to work better with Compose?