Can a playlist span multiple libraries music libraries?

Can a playlist span multiple libraries music libraries?

Yes. But only “dumb” playlists.
“Smart” playlists are based on filters which themselves can only work within one library.

Here is a test playlist which has 4 tracks from 4 different sources

  1. My music library
  2. my ‘spoken word’ library
  3. a track on TIDAL
  4. a track in a music library which is shared with me by a different Plex user

The source is indicated by the icon left of the play time.

Thanks OttoKerner. That answers my question.