Whenever I hear neurologists go on about how "free will" is a lie, I cringe.
I think there is a genuine disconnect between academia related to this topic and the reality of the situation. Academia is hard-set on putting stuff in neat little boxes. While the brain and consciousness simply doesn't works that way.
Like, playing a piano is a conscious act, right? But does the pianist calculate each and every push of a key? No. It happens automatically. But the pianist is aware of the movement, the song, and the act itself, and can stop at any moment they desire. After that, they can consciously push keys individually.
Like everything about humans, consciousness is fluid. It shifts, ascends and descends levels. It might be there for one process before vacating somewhere else right after. It moves constantly, and exists in a spectrum.
There was a stupid study where some idiot tried to measure the existence of free will by reflexive actions and concluded that it didn't existed. Yea, dumb right?
But the real problem is that the other studies are like, a notch above that one. They measure conscious finger movements, instead of reflexive ones. Then they see the neural lag of the cerebellum and the person synching -the slow rise they are talking about- and conclude that free will doesn't exists. I think you are beginning to see the problem.
There seems to be a very strong inclination among neurologists to test free will with these very minuscule things that doesn't tell anything about the workings of higher brain functions. Surprise, even a planarian can consciously move when presented with stimuli. It's as if neurologists just don't have actual conscious agency on what they are doing, and that they are trapped in this vicious cycle of conducting inadequate experiments on the nature of will because they don't have free will.
There is also the problem of trying to meaningfully measure a concept that is so nebulous, that no one has a full and satisfactory definition of it.
All things aside, I think it is simply impossible to measure something that is just a non-real concept.