Hello and welcome to the forum! 🙂
Technically the .objo format is not binary, it's a ZIP file containing XML and assets. It's documented thoroughly here:
https://docs.objo.dev/#/solution-file-format
You are correct that the current format is not ideal for Git / version control but it is conducive for newcomers to the field and for convenience / portability of code. I've added a more Git-friendly solution format to the feature list as it's actually not much of a conceptual leap for the existing solution writing code in Objo Studio:
https://feedback.objo.dev/feature/68