Poland ceded that sovereignty when they signed the Outer Space Treaty. Poland CAN use Starlink, SpaceX just hasn't offered service there yet (they only recently translated their documentation into French and support is still only in English). The service is still in beta as things are still in development. Service is available in the United States, the United Kingdom, New Zealand, Australia, Canada, and Germany.
Edit: Apparently they just added service in France today as well.