Outline's rich-markdown-editor (https://github.com/outline/rich-markdown-editor) package is pretty nice. I have used it to make some custom MD editor/CMS experiment.
It’s very valuable to be able to have the double workflow of a nice web interface alongside a plain text developer git workflow and leads to a very future proof knowledge base.
If you’re looking for more of a CMS there’s quite a few options out there, most notably static site generators like docusaurus or vuepress. Plug: I’ve built a small tool to generate the markdown from notion, which allows me to use notion as my CMS editor while keeping the generated site fully under my control. https://github.com/meshcloud/notion-markdown-cms