We previously discovered the new standalone Music app to be included in the next major version of macOS, 10.15. In that post, we mentioned the new Music app would be made using Marzipan, that lets iOS apps run on the Mac. Recently, sources familiar with the development of the OS reached out, correcting that information.

https://9to5mac.com/2019/05/09/music-app-macos-itunes-code/