Filter to show items that are not part of any playlist?

Is there any way to show all items that are NOT part of any playlist? I would like to make sure I don’t have any unseen material that are not added to any playlist.

Plex already has a “watched” indicator on every video.
You can filter for it.

Items can be played perfectly fine without being in a playlist.

Thanks OttoKerner, that is indeed a useful feature that I could not live without (well, I could but you know what I mean). However, that does not really go all the way to what I want to do.

Background: I have a lot of unwatched material, and we are a couple of people in my household with very different taste for movies. Call it wife/husband disparity if you want. So, to facilitate browsing, I put it in either husband / wife playlist. Every item is supposed to be in either husband or wife. To make sure that every item belongs to a playlist, I would want to know how to do this.

Thanks for the explanation of your use case. This really helps a lot categorizing the many requests.
Maybe you want this instead: Feature Request - Watchlist ?

Early 2021 clean-up: duplicate