Interesting that NetFlix support even acknowledged the issue - most of the time they play dumb, though its been reported to them for years.
Perhaps if someone semi-notable goes on a Twitter rant about the "autoplay on details" issue and its impact on their specific "diverse" existence, somehow within a few days it'll be a new autoplay option...
This problem happens on a new TV w/ Roku I purchased. It did not happen on the TV I was using last week. I contacted (chat) Netflix support and it took 90 minutes of troubleshooting before the agent wanted me to restate what I was reporting … and then told me that was expected behavior and couldn't be changed. It took another 30 minutes to chat with a supervisor.
Note to self: don't contact Netflix support again!
I know you already have your answer and everyone is correct. If you are looking at the splash page of what the movie is all about, it will start playing. Probably designed by young people who are impatient and are quick to read and don't like long delays in anything.