You’re right that mathematical proofs are usually published on arXiv and then in journals. But since you mentioned code: sharing code on GitHub is actually very normal in research. Even if it’s just a solver or scripts for experiments, putting it on GitHub helps with reproducibility, gives others a chance to learn from or build on your work, and makes it easy to cite. There’s no obligation to polish it perfectly—lots of research repos are just “as is” snapshots to support a paper.