You're not shy, you're just practicing shy behaviours for years!
So if being shy is just you practicing a set of shy behaviors, then confidence is just another set of behaviors you can learn.
Every movement, gesture, and word choice from great speakers is simply practiced behavior. When you watch someone command a stage, you're seeing thousands of hours of repetition.
The trap is letting these patterns become your identity. "I'm not good at public speaking" becomes a self-fulfilling story. But you're not stuck with the behaviors you've practiced so far.
Remember, everything you admire in others are just behaviors that you can learn.