That depends on the person defining it. Why can't it be the outcome my brain has determined for me to take which I subjectively understand as a self-chosen act

That depends on the person defining it. Why can't it be the outcome my brain has determined for me to take which I subjectively understand as a self-chosen action? That may well depend on my history--my emotions, memories and all the things that shape me--but those are more reasons than constraints. Isn't that like saying I want to fly, so I don't have free will if I can't?