If the universe is deterministic, it means that every particle has an infinitely predictable path. And our body and brain are full of particles which could only ever move in the predetermined way. And because our thoughts are only movements of neurone, which in turn, as everything, are made of particles, every action of ours would be predetermined and we could never decide otherwise than we did.

sometimes your brain will decide something independently of conscious thought, and then invent a compelling narrative for why you are about to do what your brain already decided you were going to do

This kind of effect can be seen when a split brain person reacts to textual commands, like "stand up" seen on a computer screen in front of them only one eye can see by standing up, but when asked verbally why they stood up they just make up some shit on the fly like "I was tired of sitting and wanted to stretch my legs"

We're just narrative machines (no, not like ChatGPT)

It could be asserted that none of our decisions are ever actually real, and its all just a series of these 'decisions' that are just invented by your brain to explain why you're doing what you were always going to do, and thus you don't have free will you just tell yourself that you do as a nice story.

I don't believe that, I think that assertion is a bit like last tuesdayism and I dislike the unfalsifiablity of it, but yeah I get the argument

I think Camus might have summed it up best when he said the only real choice (therefore, freedom to exercise will) humanity has is whether or not to commit suicide.