On an AppleTV running tvOS 26.x, go to the Settings App, scroll down to Apps, then under App Settings select TV. Here is where you will find the Auto-Play for Play Next Episode, Play a Recommendation, what to show on the Top Shelf of Apple TV (What to Watch or Continue Watching), and further down, under Video and Audio, the option to Autoplay Video Sound (as well as Streaming Video Quality and Audio Language).