Do we actually have free will? Or has the future already happened?

Do we have free will or is it all predestined? When you think about observing our lifetime from a higher dimension, you can see everything all at once. This begs the question: Is it sort of like a book where every page and chapter is already written? It's just us experiencing it page by page. Anyone outside of time could jump to the last page and already know the ending. Or is it more like the flow of a river, where life heads in a certain direction but you have some degree of autonomy to choose which embankment you steer towards, whether you flow with the current or against the current? It a