I write a lot everyday and I'm used to do it in Markdown, to avoid dealing with "rich" editors like TinyMCE and the likes. Leaving the keyboard to format text with the mouse is a bad workflow when you have to basically type all day - I first implemented a Markdown parser into a WordPress plugin and now moving to Hugo for this reason. I have seen that the wiki pages can be edited in Markdown, but I didn't find info for other fields in the website (discussions, posts, notes, etc.) and the Markdown syntax doesn't seem to be parsed.
Beside Markdown, the real goal is also to use Mermaid, which I already implemented in Hugo and WordPress. Once you declare a code block with class mermaid, you just have to load the static JS in the page to have it rendered client-side.
For Markdown is supported in Wiki only, and special Wiki blocks, but we're thinking about possibilities to optionally replace HTML with Markdown sitewide for future versions.
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As all open-source projects seem to have moved their forums to the Discuss Ruby bloatware, which allows Markdown syntax (and very efficient typing), that feature seems more and more pressing.
To be honest, I'm only ever fighting whatever JS editor you have put in Una, it just gets in the way. The feature I miss the most is Markdown code fences.