There is a long debate on whether the physicality of the brain undermines the concept of Free Will, but I will argue that this depends on an incorrect conceptualization of the concept of Free Will.
Let's start by taking apart the word "Free Will" - What does it mean to be "free"? What does it mean to "will" something? We are never truly free – we always work within the constraints of physics (I can't fly), our society (when are we allowed to drink? when are we allowed to drive? when is it alright to curse and when not?), and ourselves (what makes us angry? what makes us happy?). But we want to be able to choose.
As a person, we have desire, needs, and wants (of course, these are physical representations too, but that doesn’t make them less real), and we can achieve those things through our actions. By selecting the right actions, we achieve the things we desire. That's agency, however it comes about.
For me, the problem is that philosophy talks about "free will" as if the question is determinism vs agency, but really, that's not what scares people, and it's not what makes people nihilistic. People are really afraid of being slaves – of wanting one thing and doing another.
Wanting one thing and doing another is something we actually understand a lot about - this is the whole point of the multiple decision-making system story. You are not only the thing that can plan and think through things (Deliberatively) but also the thing that desires and is afraid (Pavlovian) and the thing that has practiced responses (Procedural). Together, these make up the you that you are.
I think the question of “determinism” is a red herring and that it sidetracks us from the real issues. Androids can have agency, as can we, because the actions we take are extremely complex functions of our pasts (our history), our personality, and the situations we are in. When stepping back to earlier causes, there comes a point where you have to say "I can see influences, but not cause, because the function is so complex" - that complexity is our humanity, and what we want to do (as individuals) is make that complex function the best it can be.
- A. D. Redish (2013) “The Dangers of Dualism: Implications of the multiple decision-making system theory for Free Will and Responsibility” Cognitive Critique 7:1-28.