This is possible through the HomePod with Siri Shortcuts to an extent, like opening apps but not sure you can tune to an actual program. Then again, I haven’t tried. You can also sleep and awake the ATV with the HomePod.
There’s a really good YouTuber by the name of Shane Whatley that has a few tutorials covering this and other HomeKit related stuff.
When I tell my HomePod to turn on (or off) the tv, it turns on/off the Apple TV, which turns on/off my tv with HDMI CEC
When I tell it « stop playing on AppleTVName » or « resume playing on AppleTVName » it also works.
But as said in the post above if you want it the open an app you have to create a shortcut.
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