It's possible "writing into the dark" would work, it all depends on how much of the structure of storytelling an author has internalized.
Like it or not, the vast majority of published stories follow a common structure, with a plot that progresses through different phases of the story. The turning points of the story tend to occur very close to certain percentages of the story; for examples see the Three Act Structure.
If you know all of that, and you know how to write descriptions, setting, realistic dialogue and so on, then you can know, by approximately where you ARE in the story, what kinds of events, scenes, and action you should be writing about next. So sure, you could make it up on the fly.
A story can begin with our main character in her normal world, doing normal things. We need to make up who she is, what she's doing, how she interacts with others, etc. We need to introduce her setting, and define reader expectations. We need to decide if there will be fantastical elements; if so we need to introduce them early.
Around 10%-15% of the way through the story, our MC has to encounter the Inciting Incident. We'll make that up when we get there; but we want it to look like an everyday problem she can solve easily enough. But that isn't going to work, and the problem will escalate.
And so on. If you have written a lot of stories, even with plotting, or weeks of pre-work, you can internalize the rules of how you write stories, and come up with them on the fly, but following your internal "blueprint" of what kind of scene or plot development you need to write next.
Kind of like an experienced tour guide that truly knows all about the fifty landmarks in her city could give a good tour of them even if they were visited in some random order. At each stop, she knows what to talk about, and how to link it to things already visited, or soon to be visited.
I don't recommend it as a starting place. Just like the tour guide, if you don't always know exactly where you are in the city and what to do there, you may end up just wandering into dead ends that don't work, and don't seem to have anywhere to go.
I have been a discovery writer for 30 years, I DO know story structure, and I still can write myself into dead-ends, and have to scrap pages and pages, and come up with something else. Typically only about half of what I write actually makes it into my final novels; but that's okay. I accept that inefficiency in the name of producing good art.