If you hold a stone in your hand and let it go it will fall to the ground, but if you hold a bird and let it go it may not land for minutes, or hours.
The argument against free will is that the bird is no less subject to the laws of physics than the stone; the apparent difference is due to our ignorance of the forces and effects acting in the case of the bird. It is, I think, clear that argument is not rigorous! As we don't know the forces and their effects we can hardly be sure they account for the bird's behaviour.
In fact, we haven't got anywhere. We neither know that physical laws do account for the bird's behaviour nor that they do not. Whichever position one takes, an opponent can challenge with 'prove it!' to which no good answer can be made.
My view is that the world contains objects - such as rocks and steam engines - that manifest simple, deteministic behaviour and objects - such as birds and people - whose behaviour is far from simply deterministic. Without prejudging the nature or existence of 'free will', objects of the latter kind appear to manifest 'free will'.
One view of free will sees it as a 'high level' function, dependent on having a brain capable of consciousness and hence 'illsusion', but I want to present a different view. Consider,for example, an amoeba. An amoeba encountering a food particle behaves in a complex but inflexible way. I don't think amoeba can be said to have free will! But more complicated organisms have a wider range of responses and have to choose how to respond to a stimulus. Successul organisms will select a good option more frequently than unsucessful organisms. Thus the power to make choices will evolve. That is to say that organisms will evolve to make choices based on present conditions, past experience and even future expectation. That is to say that if one interprets 'free will' as 'the power to make choices' then free will can be expected to arise by normal evolutionary principles.
I'm not interested in word-games that focus on whether free will is free or even if it is will. I take free will to be only a name or label for our faculty to make choices. The advantage of that is that it avoids getting bogged down in pointless semantics and turns the study of free will into a scientific study of a brain process. I think we can get an understanding of free will by studying organisms of increasing omplexity and learning how they choose between optional strategies. I expect that when we have done that, there will be no deep mystery about human free will.