IIRC, Plex considers media to be watched after you played ~90% of it. That means that ending playback during the last 9 minutes of a 90 minutes feature film will still mark it as watched… the same should be true if ending a 20 or 40 minute tv episode 2 or 4 minutes early respectively.
There’s an existing feature suggestion discussing an option to configure that threshold per library. I assume that’s basically what you’re asking for… I therefore suggest you comment/vote in that thread in order to avoid distracting or cannibalizing votes (in that case I’ll close this thread as a duplicate).
