In which case it would be random. And I think that must exclude the existence of free will.
Randomness in behavior of elementary particles doesn't exclude highly ordered and reasonably reliable systems (on limited time scales) composed of such particles. Why? Because a system composed of a large number of particles acting together is can be structured to behave in a larger orderly way.
How? The macro structure averages out the randomness on the smaller scale (on a sufficiently limited time scale, but often plenty long enough for us!).
In other wording (from about 3 or 4 decades ago in another field but a good parallel) -- "order emerges out of chaos" (quite well).
Also that a macro object (composed of vast numbers of particles) -- such as a human brain -- is
largely predictable (e.g. -- 'largely' could mean for instance more than 95% but less than 100%), that is sufficient for it to have a set of reliable characteristics.
In humans terms, we could call that "character" or "personality" -- stable, reliable... A person, distinct, distinct and mostly reliable characteristics....up to a point (less then 100% reliability) but only
largely predictable
instead of entirely predictable. So, this macro object has a clear consistent character, yet might at times do the unlikely thing instead of the more likely thing. And a structure (such as the human brain) could be built to control or even use the smaller occasional perturbations, mostly, most of them.
So, it doesn't follow that random elementary particle behaviors would necessarily cause a human personality to act random or chaotic, nor make many choices to be random, etc. The brain might (speculation) be structured, even, to take advantage of randomness.