https://www.cnet.com/news/youtube-app-coming-to-fire-tv-amazon-prime-video-arrives-on-google-chromecast/

Separately, the phone and tablet apps for Amazon Prime Video will be able to connect to Google Chromecast streamers as well as devices that run Chromecast built-in and Android TV. That change too will happen in the coming months.

These two separate upgrades to Fire TV and Chromecast streaming devices address longstanding incompatibilities and improve their users' access to YouTube and Prime Video, respectively. The upgrades also help Fire TV and Chromecast better compete against the likes of Roku, Apple TV and most smart TV systems, which have long had YouTube and Prime Video apps.