CharcoalMosquito Ultimately, a multiverse is just as deteministically closed as is a superdeterministic universe; in both cases all future change is completely pre-specified by the initial conditions of the Schroedinger equation.
What puzzles me is why you feel the need to double down and insist on your determinism axiom, especially given that nothing is forcing this interpretation and it only serves to undermine your own perfectly valid convictions about macroscale phenomenal truth.
Okay one last go – I sincerely and honestly think your definition of 'determinism', especially where you simply equate it with 'superdeterminism', is philosophically naive and reductive.
Simply put: \text{Determinism} \neq (\text{fatalism} \lor \text{superdeterminism}).
Your stubborn, naively fatalist intuition that what you call 'determinism' means that initial conditions at the Big Bang led, 13.8 billion years later, to you choosing the specific jacket that you actually wore this morning – not just because the weather conditions were fixed, but because your reasoning, preferences and control responses were also fixed in a way that makes no difference what the local antecedents were. That view – that you could not have chosen otherwise – is fatalism and its circular reasoning such that the outcomes occur no matter what the antecedents were, as everything is fixed by a global past.
Determinism, on the other hand, is precisely the opposite. It allows for local macroscale causality such that different antecedents yield different outcomes by law. Counterfactuals are perfectly meaningful in a deterministic universe and those lawful dependencies are all that your control requires (as per compatibilism/interventionism).
If it had been colder, or if I’d prioritized warmth more, I would have worn a different jacket today (it's quite warm here). Those conditionals are true in MWI just as much as in collapse theories. Indeterminism just adds noise and wouldn’t make those reason-sensitive conditionals any truer or more 'free'.
Of course, given your naively reductive notion of 'determinism', you'll have to answer: "but even your counterfactual was fixed since the Big Bang!” And yes, counterfactuals have to be physically possible in order to be counterfactuals, as in their truth values are fixed. What matters is that in this macroscopic world, within our decohered quasiclassical branch, outcome A varies with conditions B, C, D & E. That lawful dependence is what agency requires.
In a superdeterministic world that dependence fails because any independent agent's variation of antecedents stops being possible. If you want to argue against that conditional dependence, then you’re effectively arguing against explanation and control in general, and not for indeterminism.
Your reductive proposition that “IF everything is fixed by the initial global state, THEN you have no local causal power" is only true if nothing you do could have been otherwise in any coherent counterfactual – which is a fatalist premise and not a deterministic one. Your entire essay is premised on this conflation of fatalist superdeterminism with determinism, which is what makes it a philosophically naive and reductive argument.
So please repeat after me (following Laplace): "The global state at time t fixes the global state at t+n. But this global determinism does not entail that local real patterns are irrelevant or that agents lack causal efficacy to effect local changes within that globally determined evolution".