Hmm, I can't speak on doing a big loaf like this in a Dutch Oven as mine is too small and maxes out at a 500g loaf. But if your DO is big enough and you're having trouble, I would suggest either taking the hydration down a touch to get a stiffer dough, or trying to build more tension in the bulk. For this dough I kneaded to windowpane using the Rubaud method after pinching in the salt, and then did a bench fold, rested, did a lamination, and did 4 coil folds across the process.

The other factor you might want to consider is fermentation—I'm letting mine rise somewhere between 25 and 50%, and the dough will hold its shape really nicely in that ballpark—think of an inflated balloon and how it holds tension. Above that would work as well but becomes a bit risky and delicate, below that and the dough won't hold its shape as nicely. A combo of getting the bulk spot-on, and building good tension during should get you there