Plex Server Version 1.23.6.4881
Plex Player Version iOS 7.21.1 (deleted and re-installed)
iOS 14.7.1
I switched to new Download feature described here: Sync is Dead (almost). Long Live Downloads! (Part 2)
Initially after making the switch absolutely no downloads were working…playlists or individual content. I had to delete Plex App off my iPhone and then re-install from App store. After that, then I was able to get new Download feature to work. Now when I download a Playlist, it keeps everything organized as a Playlist. Appears this new Download option resolves this issue and makes Playlists available for downloaded content.
Thanks to Plex for their work on improving this feature of the software!