I've posted this before, but can't even find my previous posts, let alone any answers, so ... trying again.
I have a chromecast with google tv in our bedroom included in my Google Home network.
If I start the Chromecast manually (with the remote), and use the remote assistant, I can say "Play/Open/Watch Sportsnet". Sportsnet is an App installed on my Chromecast dongle. This works perfectly.
If I don't manually turn on the Chromecast, and say to the Bedroom Nest speaker "Play/Open/Watch Sportsnet on Bedroom TV", it fires up the TV and selects the Sportsnet channel on Youtube, which is NOT what I want.
How do I get Nest Assistant to select the Chromecast App in preference to the Youtube channel?
Answered! Go to the Recommended Answer.
I've tried that (and several variations). If the TV is OFF, it turns it on, but leaves it sitting at the ChromeCast Home page, just as if you'd never asked for a specific App to be opened.
This is an important feature, as my wife is visually impaired, and finds it extremely difficult to read the screen, so if something goes wrong, she's simply lost. She counts on doing things by memory - Hit this button, right 3, press OK etc. When that fails, she just can't recover.