1. Install vim Copilot plugin. 2. Name your file with .txt extension. 3. Write stuff.

https://github.com/github/copilot.vim

Copilot is designed for code, but it can still be used for whatever you want. I found it useful when writing latex files, even for the text explanation portions as opposed to the text markup 'code'. There was a y combinator thread on this earlier.

https://news.ycombinator.com/item?id=29920035