There’s already an existing feature suggestion thread discussing an option to add items from Plex’ Discover section to your library (optionally linking a specific service). I suggest you comment/vote in that thread in order to avoid distracting or cannibalizing votes.
There’s another suggestion thread discussing another way how to list content you own on a different platform in your library
https://forums.plex.tv/t/way-to-add-movies-we-own-digital-copies-of-to-discover/786196?u=tom80h
Unless I’ve missed some unique aspect of your suggestion, I’ll close this thread as a duplicate.
