NCweb is a reasonably small (ish) PHP “application” that will allow you to expose a given folder of a Nextcloud instance and serve documents from it as if it would have been a regular website. The folder does not have to be shared in Nextcloud. You can serve .html (HTML) or .md (Markdown) files. NCweb can be configured to render Markdown files to HTML.
Get it from Github here: github.com/joho1968/NCweb