Free will would mean that you believe in something without any ties to your environment, how were you raised up, your mental state, biological factors… etc. It would mean you started believing in something without any of those factors and just the concept of believing is predetermined by the fact that you are a human.

I don’t think you can defend such a crazy ass huge concept as free will by such a simple argument. You need to start with definition, what do you understand by free will. Is it a binary state? Or is your will free only to some degree?