I just realized that Jekyll is written in Ruby... and I don't know any Ruby. I'll check out the other options you discussed.
Somehow I confused it with Jenkins (the CI system) that is written in Java. On the other hand Jekyll is supported natively by GitHub: https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/about-github-pages-and-jekyll P
