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This is possible in a way. What kind of playlist are you trying to build?
What you want to achieve is already do-able with the standard feature set of Plex. There is no need to create collections or playlists for this. If you add this anime into a tv show library, Plex will automatically track your brother’s progress as he watches it.
Supposing if your brother has watched all the episodes so far, once a new episode is added to the server, it will appear on your brother’s start page in ‘On Deck’. He can resume watching this series whenever he wants to.
For this to work, you need to follow Plex’s standard for file names and folder organization: https://support.plex.tv/articles/200220687-naming-series-season-based-tv-shows/
Sorry, I don’t know what you mean with “initial playlist”.
You can use this how-to to make the playlist: Watch crossover episodes of several series in-order
But this still requires you to adhere to the above mentioned rules for tv series in Plex. There is no way around it.
Yes, that is explicitly mentioned in the linked article.
No, it is not out-dated.
You must use the web app. Which app are you using? Make a screen shot if you are not sure.
Remember: you need to have your media in a ‘TV Shows’ library.
Screenshot please. The whole screen.
I’ve thought of this exact process before, so I could make playlists of kid-friendly shows playing in the background as I do housework to entertain the little ones. However, one flaw that I see is the playlist is not regenerated when shows are watched. This means the watched status is pointless as it only is taken into account when the list is created. I can’t speak to the part about new eps being added when added to the library, but thought I would add this bit as it seems a logical extension of what you’re trying to do.
Early 2021 clean-up: deleted by OP
