git diff only diffs unstaged commits
git add . does not stage empty directories
if you add a new file to the empty directory it does not get tracked
a quote i like
Don’t talk about giftedness — one can name all kinds of geniuses who were not very gifted. They acquired greatness, became geniuses. All of them had that diligent seriousness of a craftsman and worked tirelessly. ― Seneca, Moral Letters to Lucilius