"GitHub Pages is not intended for or allowed to be used as a free web hosting service to run your online business, e-commerce site, or any other website that is primarily directed at either facilitating commercial transactions or providing commercial software as a service (SaaS)."
So it's great if you want to host a personal site / blog or some other non-revenue-generating website, but for anything more than that you could run into issues.
[0] https://docs.github.com/en/github/working-with-github-pages/...