bake VS gbt-player

I agree in case of cmake, but not in case of e.g. meson (or all other build systems the specification files of which are not scripts). But we also have to keep in mind that JSON is just the basic syntax, but the interesting stuff is built on top; it's like XML, which - as we know - can quickly become human unreadable and complex; JSON has simpler constructs than XML of course, but what you do with JSON is even though subject to specific usability assessment; a specification language is not automatically more usable because it is based on JSON. And also the other contemporary build systems abstract e.g. compiler differences away. I would compare your approach to e.g. Qbs or https://github.com/SanderMertens/bake.

This video (plus the next part in the playlist) has an intro to creating music using GBDK and GBT Player https://www.youtube.com/watch?v=7l93RP986Zo I gather that hUGEtracker and hUGEdriver https://github.com/SuperDisk/hUGEDriver are the new preferred music tools with GBT player https://github.com/AntonioND/gbt-player being an older, more complex option (I haven't used them enough to form an opinion).

I want the .mod file (or some equivalent transcription of the notes/instruments that I could import or convert) so that it will work with GBT Player. I'm doing a project which uses GBT Player to play the music.

If you're asking how I made the game itself, I wrote it from scratch in GBz80 Assembly. I'm using RGBDS for assembly. Most of the assets are converted to a usable format with custom Python scripts. The music is made with OpenMPT and converted/played with gbt-player. The map tool in the video is a collection of C# scripts that generate and export assembly by parsing the Unity scene. Here's what the file looks like.