New toggles in Settings > General allow you to decide whether to auto-play the first video when students enter a lecture, and/or auto-complete the lecture when students finish the final video.
Toggling these settings ON will cause the automatic actions to happen. By default, for existing schools both of the toggles are off.
For new schools, autoplay is turned on by default while autocomplete will be turned off by default.
Any schools that used custom code to autoplay videos or auto-complete lectures before this update should remove that code now so it does not interfere with the new function.