I've read about this a few times. If you disable it once, does it get disabled permanently? Because Netflix (unlike the Amazon Prime Video ads) never plays trailers with sound for me.
> auto-play next episode "feature"
I'd certainly call it a feature. I'd hate having to manually click every time I want to see a new episode.
I have a recent AppleTV, which doesn't have any way to disable auto-playing trailers. Same for my previous STB (Roku). This is a somewhat new feature, so some older STBs and Smart TVs don't have it, but that's just because they can't be updated to the latest version of the Netflix app.
You can disable auto-play next episode across all interfaces and devices in the settings on netflix.com. I just wish there was an equivalent switch for trailers.