Force all Apps in Landscape mode
Hello I was able to make all my apps on the FireTV start in landscape at launch.
Ultimate Rotation Control 5.30
Ultimate Rotation Control license (purchase from the Playstore)
Extract the apks(app and license) from a rooted device using Root Explorer
Push both onto the FireTV
In app, set the Global setting to portrait mode.
All your apps that tend to launch in portrait mode now start in landscape mode.