Reddit users thevincentasteroid and MMD3_ posted about an auto-playing video ad (with sound) on the home screen. The ad is for Chicken Tender Wraps from Carl’s Jr. When it begins auto-playing, it pushes all the other UI elements out of focus and goes almost full-screen, returning to the home screen after it has played through once.
I use a Chromecast with Google TV everyday and I do not receive autoplay ads on the home screen. You are free to disable ads on the home screen in the settings and you are free to install third party home screens.
In fact, the only interaction with the home screen that is required is when I see it briefly before pressing the Netflix button on the remote which I have remapped to Plex or jellyfin using the button mapper app.
Even with the default home screen you do not see auto play ads unless you select them and continue watching.