The work of Schopenhauer, cf. previous post, is also a good commentary on the free will question. In general transcendental idealism of the Kantian variety suggests an outline of a solution. Much of what is debated is, as Schopenhauer makes clear, under the assumption that a kind of monistic physics, that is, just plain physics is the source of all possible explanation. But we could never be sure that is so, and the evidence suggests that as we ascend from physics there are more and more problems without physical derivations. On the question of free will, pace Schopenhauer, we are in the realm of two systems levels at work. The phenomenal versus thing-in-itself level is not the source of free will. Free will would perhaps decide on an option which then takes phenomenal form and becomes a causal stream. The endless verbiage on the subject vanishes in one line, given this possibility.
Note that we cannot specify the thing-in-itself level of the will, which reaises the question of the noumenal/pheomenal that dogs Kantian thinking. But it seems the right approach in general. We do not ‘know’ the will: it is inferred from the overall context of the phenomenal. The thing-in-itself is not resolvable to ‘knowledge’.
The value of Schopenhauer is that we don’t derive ‘will’ (free or not, most discussion nevers onsiders unfree will! The latter is not the same as saying ‘free will’ doesn’t exist) from physics: ‘will’ is an independent category in nature. The idea of an ‘unfree’ will is commmon in many walks of life. We are free/unfree to break laws, etc… Legally we assume a ‘will’ that can be in some contexts ‘unfree’ in some sense.
Actually, as noted, beyond the resolution created in Kant/Schopenhauer, there is the simple possibility that physics doesn’t describe reality at all well and that the brand of physics we now use, like the now long gone Newtonian brand (still useful), has a gap in its explanations. There could be some larger theory that takes into account the issue of freedeom/causality as an intrinsic dyad.
If you study WHEE at history-and-evolution.com you will see Kant’s challenge, which intimates something like this in the idea of the ‘causality of freedom’. The latter is an oddity arising in Kantian thinking, and finds some meaning in the macro effect in WHEE.