I use Apostrophe markdown editor. It’s basically a plaintext editor with Markdown syntax highlighting and a rendered preview mode. It is the same formatting language you can use for posts and comments on Lemmy (and the other place).

Honestly, I’m just obsessed with Markdown. You can write it anywhere you can type. It’s just structured plaintext that you can easily convert to other formats (html, odf, pdf, etc.) Write it in Notepad. Use it text messages. Put it on Facebook. There is no native support for the format in any of these places, and it doesn’t matter.

I do all my writing in Markdown now. It keeps me focused on my document content and structure.