What is Cause

Let's say plunging this knife into my chest, X, has a 99% chance of killing me, Y. Let's say that this knife actually does kill me. Therefore, plunging this knife caused me to die. We use cause here to show that X is sufficient to cause Y, and that Y did actually happen.

In the 1% chance that this knife does not end in my dying, then X did not cause Y. X is therefore not a necessary cause.

Free will seems to be a problem only when causes in a causal chain are necessary.

But such probabalism should not be present in the mechanistic universe unless quantum probabilty or some other similar mechanism were introduced into the system.

But doesn't a high probabilty, even in a probablistic universe, cause a problem for free will? Isn't it a problem when your actions are caused at least 99% of the time?