Question: Smart Playlist on iOS only, not iTunes
Simply put, iTunes is a terrible application. Up until iTunes 6-8, it was decent. Now it is bloated. Apple has ruined it, by taking features away, or by making it more difficult to use the app. It's like Apple only thinks people will use their device in the very limited ways Apple has predicted.
I used to be able to create and edit playlists on the iOS device from iTunes. Now, I can't even see the playlist on the device in iTunes. Guess what, I don't want my music library on my Mac, nor do I want all that content on my device either. I want to make a Smart Playlist for my iPhone, but that isn't possible. I instead have to make the Smart Playlist on iTunes, copy it to the iPhone, and end up with all that extra stuff on the iPhone that I don't want there.
Let me create, edit, manage playlists on the iOS device - smart or otherwise - on iTunes.
iPhone X, iOS 11.2.5