Do you care to elaborate more? I am genuinely curious about your opinions.
Have you read/listened to any of Dr. Robert Sapolsky's material on free will? I am curious what you think of his position on the matter.
If the universe were not deterministic, for reasons like non-deterministic physics, souls existing, etc. you would potentially see difference between the two as they played out separately.
Another way to think about determinism vs non-determinism is that if something is deterministic, then if you have perfect information about it, you can predict it’s future states exactly. On the flip side, if something is non deterministic, no matter how much information you gather about it, you will never be able to exactly predict its future states (only probabilistically).
Einstein is not so subtly telling us “god doesn’t play dice”, that there are no random physical properties of the universe, and that magic (like souls) doesn’t exist, in his opinion.
Free will means we have a choice in what we do next, but if we go and examine your carbon copy in the other universe you will see they did all of the same things you did. Furthermore if we were granted perfect information about the universe and had a good enough gpu, we could from the physical principles of the universe predict the future state of everything in the universe until the end of time, including all of your future choices, hence no free will.
My thoughts are that people are mixing up the human concept of free will — freedom to make decisions based on how you feel and what you know - with determinism, that the first state of all matter in the universe determined all future states of the universe, and that these are inevitable. The fallacy is that free will in the sense of determinism is only important to human decision making if we have perfect information about the current state of the universe, which we don’t - so until we do, we have to keep guessing what happens next.
Given how often we delegate whatever free will we have, intentionally or otherwise, it's easy to conclude (or at least suspect) that whether or not it exists in the first place simply isn't an interesting or important question. Sure, we might have free will, but if we do it's almost overwhelmed by noise.
As far as Sapolsky goes, it's fine to argue that free will is an illusion. But it doesn't follow that we should stop believing in it. Actually, belief in free will is adaptive. Concepts that follow from free will such as punishment, guilt, blame, etc are extremely effective at promoting pro-social behavior and it's not clear how they could be replaced.