Apple filed a trademark on January 3 that shows a Dark Mode version of the Apple Music icon.
Dark Mode Icons
The icon is the same music logo, but with black space around it instead of white space. It’s a live trademark application and awaiting examination. It’s currently the logo for Apple Music for Business, but I wonder if we could start to see more dark mode icons.

Apple’s trademark filing showing dark Apple Music.
The mark consists of a black square with rounded edges with a blue, purple, and pink stylized musical note in the center.
This tradmark registration is intended to cover the categories of
Last year I wrote an article where I made mockups of iOS dark mode icons, and I hope Apple considers it for iOS 14.

My mockup of Dark Mode iOS icons.