Hopefully this post saves people some time.
I just confirmed with Netflix that it is currently impossible to disable autoplay from the details page of a show. The details page is the main page of a show where you can rate the show, browse episodes etc.
So, don't waste your time trying to solve this. Instead call Netflix and ask them to submit a complaint on your behalf.
Maybe if enough Roku users complain they will fix this issue with the Netflix Roku app.
