Even when you're connected to a VPN, Amazon can still see your activity within their own apps, like Prime Video or Freevee, because you're logged into your Amazon account. However, a VPN completely blinds
your ISP to your streaming habits and prevents Amazon from tracking what you do in third-party or sideloaded apps outside their ecosystem (aka, not on their hardware). It also stops Deep Packet Inspection (DPI), which is the fancy term for your ISP snooping on your traffic to throttle your streams.