Randomness is not an objection to determinism. The problem is not that decisions can not be predicted, the problem is that some people think decisions don't exist. For that vision is irrelevant if they happen by chance or by rules.

The real answer is that decisions exist in a different frame of reference. Some philosophers are stuck in a model in which decisions were taken by the soul, an inmaterial entity. So if decisions are generated by physical processes, they're an ilusion.

But that's as idiotic as it can be. Our brain is a material system and of course decisions are generated by physical processes inside it. The interesting question is how much of us is malleable and how we can make our decisions to change ourselves and our own decision making process.

Where does the randomness come from? If we could rewind the universe back to the same starting conditions, would it be any different the second time through and if so, where did that difference come from?

If you suppose an infinite multiverse where every possible thing happens in parallel, a typical observer will find themself in a universe with events that seem random. There are a lot more random-looking numbers than orderly-looking numbers.

Randomness in the map does not equal randomness in the territory, i.e. randomness may be a feature of our world-model, not the world itself.