This sounds like a recursive (and effective) solution to the problem.

I can plot an entire storyline (screenplay) in advance, but the result is thin and uninvolving. But usually I do know what I want the very ending to be. Still I have the problem of the vast majority of the storyline.

I think our brains / minds use a combination of analytical (plotter) and intuitive (pantser) approaches to create the story, and if we use just one method, we’ll never achieve wholeness in our storytelling.

Your approach is to plot some, then pantser back over that stretch, then plot another stretch, pantser back, etc. So neither plotter nor pantser takes over the entire process. Because you pantser before bed, when the analytic side is starting to go to sleep, you’re less likely to overthink the pantser stage, since it won’t feel to the judgmental analytical side that you’re backtracking.

Thank you for sharing your experience.