Originally, the free will had to do with humans developing the conscious chocie to act with or apart from instinct. The animal acts using instinct, since this behavior is programmed within the brain, having been optimized by evolution over millions of years. Free will appeared when human were able to modify long term programming via will and choice.
Free will first appears due to the onset of human subjectivity, not objectivity. In other words, instinct is a product of millions of years of optimization. The objective person can see the merit in this test proven programming. Subjectivity, by being out of touch with cause and effect, allows one to chose differently, thinking it is even a better choice without knowing the difference. It only has to feel right.
This original free will, because it was subjective and did not have to be in touch with cause and effect, was like a random idea generator that allowed will power to grow in the form of a widening range of choices.
Further progression within free will become more objective. In other words, of all the possible random subjective free choices, not all are optimized. Objective free will tries to reduce the random possibilities to a narrower set o fchoice that are more optimized. That is still will power and choice.
In the limit, the combination of subjective free will to generate random choices and objective free will, to narrow this set for optimization, should eventually lead to a new version of human instinct.