Play Music has been in limbo since YouTube Music relaunched two years ago. As the latter streaming service gains new features — like last week’s Now Playing redesign and discovery revamp, the Play-branded app has been functionally and visually frozen. Users have had no choice but to keep using it as switching would require starting their audio experience from scratch. That’s changing today as Google starts letting you transition Play Music libraries to YouTube Music.
Google Support: Transfer your Google Play Music account - YouTube Music Help