Hello.
You download apps for the Fire Stick via your Amazon account - i.e. all apps that you find on Amazon.de can be downloaded to the stick. I didn't find it on Amazon - so I think not. But Sky has its own stick, or via the app on the TV.
In general, you can't watch any pay services (AmazonPrime, Netflix, Disney+ etc) for free. To be able to log in, you need an account + subscription with the corresponding provider.