There’s an existing feature suggestion asking to support a model like STRM files. Those are basically files you can store in your media library which point to the URL of a video.
Similarly there’s an existing suggestion asking for an option to link media from other platforms (not like those will allow something like this).
Keeping in mind that Plex is aiming to be a platform for media you own (aside of online media sources contributed through Plex), I consider supporting such external URLs will be quite a significant change (and one with a lot of licensing/legal implications).
TL;DR: I suggest you comment/vote in the existing suggestions to avoid distracting votes by having duplicate versions.
