That is, Free Will as a concept doesn't really make any sense. Does Free Will mean if exactly the same situation happened twice, the person might choose different things? But its somehow different to just being random? And when does exactly the same situation every happen twice anyway? Its an incoherent concept.

In my head, I have sortof redefined 'free will' like this:

The world is a mass of cause-and-effect chains. For a given object/being, if you were to 'trace' those cause-and-effect chains, would most of the proximate links in the chain be within the object/being, or outside of it? e.g. a rock can fall and roll around if pushed, those chains of cause-and-effect are mostly outside it. Us, as humans, choose to do things using our brains, so the chains of cause-and-effect (or the first bits of the chain at least) are within our brains. Naturally if you trace the cause-and-effect far enough you will get to some external cause (memories of previous events, learning etc). But if you look at the proximate cause-and-effect chains, they're mostly in our brains. That - for me - is roughly what I take Free Will to mean. The center-of-gravity of recent cause-and-effect chains reside within us. We have it, most animals have it to varying degrees. Rocks dont have it.