Ok, then you need to link 'free will' to the state and function of the system.
A physical system that functions according to architecture is not a matter of its Will, be it conscious or unconcious
That World works according to its own principles does not equal free will. The brain functions according to its architecure, not its will.
To say a brain making decisions without coercion is an instance of free will is asserting one's own terms upon a system that does not function on the principle of will, be it conscious or unconscious.
That the world functions unempeded does not equal free will.
That the brain may function unempeded (absence of coersion) does not equal free will.
Besides that, without regulative control and actual alternatives (not possible in a determined system) there is no actual choice, the course taken is determined and any reference to ones 'choice' is an illusion borne of insufficient information: one is not aware of the absence of realizable options.
"Free will" as I am using it, refers to a person deciding for themselves what they will do, while free of coercion and other forms of undue influence. The brain is the origin of these notions (and all notions, for that matter). So, these notions, by your description, would be the necessary result of one brain's architecture interacting with other brains according to their architecture.
Possibilities (alternatives) are causally necessary notions that the brain created to deal with practical matters in the context of uncertainty. Possibilities exist solely within the imagination. For example, we cannot drive a car across the possibility of a bridge. But the notion of possibility is essential, because we cannot build an actual bridge without first imagining a possible bridge.
Within the domain of human influence (stuff we can make happen if we choose to), the single inevitable future will be chosen by us from among the many possible futures that we imagine. Ironically, we get to choose what becomes inevitable.
Yet within a determined system, there is no actual deciding. There being no possibility of an alternative action in any given instance in time, the result is inevitable and our reference to a decision being made refers to surface appearance....the world progressing on the principle of the specified way things are at a time t and the way things go thereafter being fixed as a matter of natural law.
1- If determinism allows multiple options to be realized by an agent, as a matter of choice, why call it determinism?
2- If freedom does not require the possibility of realizable options, that the world proceeds along a determined, singular, course of events, why call it freedom?
3- If 'freedom' does not require a means for the selection an option from set of realizable alternatives, what is freedom?
4 - Without regulative control or realizable options, why call it free will?
Ironically, when someone uses phrases like "actual" deciding or "really" choosing, it often flags a switch from speaking literally to speaking figuratively. We can check for this by stepping back and observing what is actually happening in empirical reality.
For example, choosing is a real event that takes place in empirical reality. Choosing is an operation that inputs two or more options, applies come criteria of comparative evaluation, and outputs a single choice. A woman goes into a restaurant, browses the menu, and places her order. She literally has a menu of options and she literally told the waiter, "I will have the Chef Salad, please". So, we empirically observed the multiple options and the single choice. As to the evaluation phase, we can walk up to her and simply ask, "Why did you choose the Chef Salad?" She says, "I was tempted by the cheeseburger, but I had eggs and sausage for breakfast, and I wanted to balance that with some veggies for lunch. The Chef Salad will help me meet my dietary goals and it looks tasty".
So, the event we call "choosing" actually took place right there in front of us, we objectively observed it happening in empirical reality.
Was her choice determined? Yes. It was determined by her own purposes and her own reasoning. And, we may assume that her own reasoning was the inevitable result of prior events, events with their own prior causes, going back as far as anyone can imagine (I like to use the phrase, "causally necessary from any prior point in eternity"). But the most meaningful and relevant causes of her choice were the thoughts and feelings she experienced while making this decision for herself.
So, within a determined system, actual deciding does happen. The process of deciding was just as causally necessary as the choice. And the fact that she would be the single object within the physical universe that would make that choice was also causally necessary.
Let's take the questions now:
"1- If determinism allows multiple options to be realized by an agent, as a matter of choice, why call it determinism?"
Well, determinism asserts that we live in a world of perfectly reliable cause and effect, where each event is the reliable result of prior causes, and each of these prior causes is the reliable result of their own prior causes, going back as far as we can imagine. We are assuming that there is such a chain of prior causes leading up to her deciding to eat at that restaurant, reading the menu, considering her options, and making her choice. And her choosing operation was also deterministic, following a reliable chain of reasoning, leading to her choosing the Chef Salad from her many options on the menu.
So, apparently, the notions of determinism and the notions of deciding for ourselves what we will do, are not contradictory, but are in fact compatible.
"2- If freedom does not require the possibility of realizable options, that the world proceeds along a determined, singular, course of events, why call it freedom?"
But her options were in fact realizable. The chef at the restaurant was able to prepare any of the items on the menu. All of them were real possibilities, things that could happen if she chose them. She imagined having the cheeseburger. She imagined having the salad. Real possibilities exist solely within the imagination, and that is were she evaluated her options. None of them would become an actuality until she chose them and the chef prepared them. That's how real possibilities work.
Was she "free" to choose either option? Free from what? Did anything meaningful or relevant keep her from choosing for herself what she would eat? No. So, apparently she was in fact free to choose for herself the Chef Salad.
The terms "free" and "freedom" are meaningless unless they reference some meaningful and relevant constraint, something that actually constrains us from doing what we want (meaningful) and something we can actually do something about (relevant). Is causal necessity a meaningful or relevant constraint? I don't think so. What we will inevitably do is exactly identical to us just being us, choosing what we choose, and doing what we do. And that is not a meaningful constraint. Nor is it something that anyone can, or needs to be, free of. So, bringing it up is usually irrelevant.
"3- If 'freedom' does not require a means for the selection an option from set of realizable alternatives, what is freedom?"
Freedom is the ability to do what we want. Freedom requires reliable causal mechanisms that enable us to do what we want. Right now, I want to type my thoughts in this comment. This requires a working brain, working fingers, and a working keyboard. If any of these mechanism were unreliable, I would not have the freedom to do what I wanted.
"4 - Without regulative control or realizable options, why call it free will?"
We actually need both, so it's fortunate that we have both. We need the ability to control what we do through reliable causal mechanisms. We need the ability to choose for ourselves what we will do. Free will is when we decide for ourselves what we will do, while free of coercion and undue influence. Most of the time we are neither coerced nor unduly influenced by someone or something else. So, most of the time we are
free to choose for ourselves what we
will do.