The origin of biology

[Esquilax]

The presence of free will suggests a possibility of the presence of supernatural phenomena, you can't deny that.

Sure I can! Mostly because you haven't bothered to A: define free will, B: demonstrate that it exists, C: explain what in it is suggestive of the supernatural, and D: explain why you think a natural explanation for it is less parsimonious than never-evidenced magic. You've got a long row to hoe before I'm obligated to entertain your- as of now- bald assertion.

Even if you oppose this view, you must allow at least a small percentage (maybe 20%? - just an arbitrary number) for its likelihood.

Nope. Probabilities aren't just pulled out of someone's ass because they can't explain a given phenomena, you know. They're actually determined based on data and evidence, not simply "I can't explain free will, so maybe it's magical." Without a means of determining the probability of the supernatural, I have no reason at all to assign it a positive probability, which brings us to...

Therefore, there does exist the possibility of supernatural phenomena.

Possibility requires more than just a bare assertion based in an argument from ignorance. There are actually ways of determining whether things are possible, you know, and you aren't using any of them. You're just pointing to a gap in our knowledge and saying "maybe the supernatural is in there?" which, I mean... no. Not until you've first established that the supernatural is even contained within the set of things that could exist. You're attempting to put the car before the horse, and then pretending that the cart is the horse.

likelihood is not the same as possibility.

If A has a  90% likelihood and B has a 10% likelihood, they are both possible.

Without appealing to the lack of a natural explanation for one or more observations of the real world, how did you determine that the supernatural had a positive likelihood?