Let’s get the bad news over with first: no matter how much you write, it will probably never become the kind of mindlessly automatic task for which you’re fully free to zone out.
In other words, writing steadily for an afternoon will never be as meditative as a long drive down an empty highway. You have to keep filling the progress bar yourself. Seated at the keyboard, every moment a writer spends mentally compiling a grocery list or critiquing the coffee shop’s playlist is a moment that zero writing is done.