Throughout the Plex interface when selecting multiple files there are multiple options presented, typically including the “Add to Playlist…” option. Using this option I can build multiple playlists. However, If I want to add multiple media items from one playlist to another playlist (selecting multiple in the web interface), there is only the option to remove them from the playlist.
The expected behavior would be to provide the additional options in the top menu bar, as you would typically find when selecting multiple files. In addition, there would be a “Remove from Playlist” option when the user is inside the playlist views. The typical options are Play, Shuffle, Add to Playlist, Edit, Sync, and More(…).