Discussing Libet's (1985) experiment. While we prefer to believe that we have willed our hand to rise, our intention, there is a precursor in the subconscious, the readiness potential, that can be measured using EEG and that precedes the hand movement and the reported time at which subjects noted their intention to lift the hand. The conclusion is that intention (and thus free will?) is manufactured after the event. See also (Rosenberg 2018, p.99).
Libet, B. (1985). Unconscious cerebral initiative and the role of conscious will in voluntary action. Behavioral and Brain Sciences, 8(4), 529–566.
Rosenberg, A. (2018). How history gets things wrong: The neuroscience of our addiction to stories. Cambridge, Massachusetts: MIT Press.