Latest Amazon Basics Fire TV (2020) user agents:

User Agent	Browser	Platform
Dalvik/2.1.0 (Linux; U; Android 7.1.2; AFTBU001 Build/NS6703)	Android Browser	Fire OS 6
Dalvik/2.1.0 (Linux; U; Android 7.1.2; AFTBU001 Build/NS6711)	Android Browser	Fire OS 6
Mozilla/5.0 (Linux; Android 7.1.2; AFTBU001) AppleWebKit/537.36 (KHTML, like Gecko) Silk/96.2.18 like Chrome/96.0.4664.175 Safari/537.36	Mobile Silk 96	Fire OS 6
Mozilla/5.0 (Linux; Android 7.1.2; AFTBU001) AppleWebKit/537.36 (KHTML, like Gecko) Silk/96.1.237 like Chrome/96.0.4664.128 Safari/537.36	Mobile Silk 96	Fire OS 6
Mozilla/5.0 (Linux; Android 7.1.2; AFTBU001) AppleWebKit/537.36 (KHTML, like Gecko) Silk/118.7.1 like Chrome/118.0.5993.155 Safari/537.36	Mobile Silk 118	Fire OS 6