It is tempting to take the view that Schopenhauer proved with his essay, On the Freedom of the Will, that the spiritual proletariat has no free will. If you go to the heart of what this prize winning essay really wanted to achieve however, you will realize it cannot achieve anything on its own, because its reason to exist was to shed light on his main body of work:
1. His doctoral dissertation On the Fourfold Root of the Principle of Sufficient Reason, which extended the academic achievements of Immanuel Kant.
2. His magnum opus, the nigh impenetrable The World as Will and Representation, which changed the face of philosophy forever.
The essay itself is the perfect introductory work to philosophy because right from the opening bell you will be engaged in the battle for or against determinism, a battle still fought in classrooms and among fellowships today.
As far as philosophy in general is concerned there is also great joy in Hume, Locke, Hegel, Kierkegaard, and of course Nietzsche, who is controversial but a pleasure to read, and would have made a fine literary artist (that’s exactly what he was, really, spake Zarathustra; not so much a philosopher as a genius storyteller on the verge of sagedome).
If you have experience in the field, with even a moderate understanding of the deeper meanings of Schopenhauer’s ideas, are you really surprised by any of these observations? You need a “serious” précise, but your mistake is wanting to apply it outside of academia. You wanted to be a know-it-all gunslinger, but here you are, looking for random guidance from a house on the prairie. Thusly consider: free will is a spectrum.