I am a long time Jekyll user and I still think it's a great tool for blogs, but by far the best SSG for documentation websites I have found is Docusaurus. (https://docusaurus.io/)

I resisted trying it for the longest time because I didn't want a JavaScript based tool, but I am glad I caved. It's so easy to get started, crazy fast, and the sites are absolutely beautiful out of the box yet easy to customize. The mdx support is awesome too.