Better option: Apple's Notes.app which comes included, you can also make a note full screen and it looks almost the same. On top of being iCloud synced to all your devices for free.
Unfortunately, Notes is incredibly slow. Even with just a few hundred pages of text in a note, and no images or complex formatting, it stutters on text input on an iPhone 15 and, while not stuttering in input, is jerky and slow to scroll on an M1 MacBook Pro. That means that there’s management overhead — going back and editing notes to split them up — to keep it usable, which is almost exactly contrary to the point of this article’s type of writing-and-writing-alone tool.