That setting has nothing to do with it even if some people here seem to think it does.
I don't believe there's any way to disable it within "The Roku Channel" unless someone has an idea other than the aforementioned Accessibility setting (that only stops autoplaying while browsing or upon app launch).
Source: https://developer.roku.com/docs/developer-program/media-playback/autoplay.md
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.