So I'm confused on how this is possible.

1. If determinism is true freewill does not exist:

If determinism is true, then every event has a cause, and every cause has a unique effect.
If every event has a cause, and every cause has a unique effect, then our actions are also determined.
If our actions are determined, then we do not have free will, because free will requires us to be able to choose between different possible courses of action.

2. If the time evolution is probabilistic:

The argument that probabilistic time evolution undermines free will goes as follows:

If our actions are determined by the laws of physics, and the laws of physics are probabilistic, then our actions are also probabilistic.
If our actions are probabilistic, then we do not have free will, because free will requires us to be able to choose between different possible courses of action.

I find it strange that the phenomena of determinism - D's validity actually informs us on freewill. Because if D is true I conclude freewill is false. But if D is true I conclude freewill is false.

Naively I'd just conclude the status of D does not inform us about freewill but that's confusing. What logical error am I making?