Markdown Gutenberg Block
I really like Markdown. It's the easiest way I've found to quickly write blog posts. And while WordPress has bumped up its support for Markdown, it's still not as good as some of the other programs out there.
And that's what this plugin is. It wraps SimpleMDE in a Gutenberg block so you can edit your posts in Markdown and have it converted back to HTML when displayed.
Download the latest release from GitHub.
Login to your WordPress site and click on Add New Plugin and then Upload Plugin.
Upload the zip file you downloaded from GitHub and activate the plugin.
Once activated you should have a Markdown block in your WordPress editor.