Pandoc https://pandoc.org https://pandoc.org is described as a Universal Document Converter. It can convert markdown (and quite a few other formats) into ePubs,

Pandoc https://pandoc.org https://pandoc.org is described as a Universal Document Converter. It can convert markdown (and quite a few other formats) into ePubs, PDFs, doc files, etc. If you need to produce eBooks, Pandoc is a more powerful tool. It's been around for quite a while, and it's very well documented.