I wrote a Scriptable script that allows you to publish a text/Markdown post to Micro.blog from any text editing app, using the iOS share sheet. It works via the Micropub API, which means that, with a few tweaks, it can be modified to work with other Micropub endpoints, as long as they support app token-based authentication.
The code and some documentation are available on its GitHub repo, mjdescy/scriptable-publish-to-micro-blog.