Why am I missing some of my playlists in SongCapsule Quiz?
If you’ve created a playlist in the Music app that’s not showing up in SongCapsule Quiz, you may need to publish it to Apple Music.
Steps
Open the playlist in the Music app.
Tap the ellipsis icon in the upper-right corner.
Tap Share Playlist…
This action alone should publish the playlist to Apple Music and make it available in SongCapsule Quiz.
Note: Nobody will see your playlist or its content on Apple Music as long as you don’t share the playlist link or make it publicly available on your profile.