She's never going to have full control really. Filmmaking is a collaboration, and from FBAWTFT onwards, story sessions after Jo was done with a draft have been her, Yates and Kloves reading the script out loud, rewriting it, developing it, etc. I guess you mean without possible interference (though we never got proof of it) from the studio?
I would say that's one element that a lot of people don't seem to have taken into account, that Jo has all the power here with Zaslav publicly saying he wants WW TV series (he met face to face with Jo about it in early 2022) and more Harry Potter. So they're gonna have to keep her happy.