You can now officially move playlists between Apple Music and YouTube Music. Apple has published two help documents (linked below as Resources) that explain what you need to do to switch from one service to the other.
Before you ask – no, there is no official way to go from Apple Music to Spotify or Spotify to Apple Music. For now, it’s just Apple Music to YouTube Music or YouTube Music to Apple Music.
Please note that only playlists you’ve created (including collaborative playlists you own) will transfer. Music files, non-collaborative shared playlists and curated playlists, and folders into which you’ve organized your Apple Music playlists will not transfer.
If an Apple Music playlist you’re transferring contains podcasts, audiobooks, or user-uploaded audio files, those won’t be transferred—only the songs in the playlists will. Of course, if the service you’re transferring to doesn’t have specific songs, they won’t be transferred.
The entire process, regardless of direction, should normally take a few minutes, but it could take up to several hours depending on how many playlists you’re transferring. Full instructions on how to transfer can be found in the resources below.