Thanks for bringing your feedback to the Idea Exchange.
I've closed this idea since it doesn’t meet one of the Idea Exchange Guidelines, namely point 5: “Make sure your idea is clear”.
It's currently already possible to use the desktop app or web player to create playlist folders, which will show up on your desktop, web, and mobile devices. Could you describe how you'd like to see it function differently? You can find more information on how playlist folders currently functionhere.
If you'd like to see playlist folders function differently, I would encourage you to submit a new Idea with more information, making sure it adheres to the above guidelines.