Describe when the unwanted playback begins
A trailer starting while you browse and another episode starting after the credits are different events. Before changing anything, identify which one interrupts your viewing. A useful description is “a preview begins while I move between film tiles”, rather than simply “Netflix starts by itself”. This determines which control to review and gives you a clear observation to compare afterwards.
Check the two profile preferences
Netflix documents Autoplay Previews and Autoplay Next Episode separately. Both can be reviewed for the intended profile through its browser playback settings or supported mobile profile controls. Its preview documentation also notes that iPads and some older television devices do not support preview autoplay. A missing preview on that equipment therefore does not show that the next-episode preference has been disabled.
Test the same event on the intended profile
For example, someone may want a quiet browsing screen while keeping consecutive episodes for a planned series session. They can disable previews without treating this as a request to stop episode progression. Someone wishing to stop after one episode should inspect the next-episode control instead. Confirm the profile name before saving, especially on a television shared by several people.
Allow the changed preference to reach the device
Netflix says a profile switch away and back, or signing out and in, can refresh these changes on a device. Start with the smaller profile refresh. Then reproduce the original event rather than interpreting an unrelated silent menu as success. Keep note of the control changed so the preference can be restored if the resulting behaviour does not suit the viewer.
Questions, answered
Does disabling previews disable the next episode?
These are separately documented controls; inspect the next-episode preference for that outcome.