You are discussing whether an agent is “free” in the sense of “unconstrained”. What I’m talking about has absolutely nothing to do with that.
I assume almost nothing, but however our decisions are made, they must be made somewhere. We can even allow the existence of mind-body duality, of a soul, whatever - I assume nothing about what exists and where or how we make decisions, or about the physical mechanisms, but for shorthand let’s use “brain” to denote the decision-making part of us. I only ask that we must be careful not to make the mistake of a combination of petitio principii and the homunculus argument, assuming that there is some independent sub-entity within the brain with free will, because then it just reduces to asking how that sub-entity makes decisions.
So how are decisions produced? There may be random elements that may cause uncertainty and variation, but nobody thinks rolling a dice is free will. That leaves deterministic reasons. Really, logically, what else is there in any conceivable universe other than deterministic elements plus stochastic elements? So, if a decision is made for reasons, how can it possibly be that precisely the same data input into a brian in precisely the same prior state can ever produce a different output (setting aside random variation)? It just makes no logical sense.
Moreover, there is simply no observable event that has ever occurred in the history of the world that corresponds to the notion of somebody “doing something different in precisely the same circumstances”, because we only get to run history one time. We have an incredibly strong internal illusion that we could have done something different if we re-ran history, but we have no evidence whatsoever to back up that illusion.
Thus, as I say, what is usually called contracausal or “spooky” free will - the notion that we could have done otherwise in precisely the same situation - is simply an incoherent concept. The reason that it does not exist is not empirical. It could not possibly exist in any universe because at heart it’s nonsense.
The number of philosophers who believe in contracausal free will is to a good approximation zero. Yet, the vast majority of people still do believe in it, imo just because they haven’t thought it through carefully. Some philosophers (such as Dan Dennett) have written books supporting the notion of free will - but they have just re-defined it to mean something else, “lack of constraint” or whatever. Imo they distract from the important fact that what Christians and almost everyone else means by free will (the contracausal kind) is simply nonsense.