Google previously announced that they would be shutting down Play Music. If you want to continue streaming music you will need to transition to YouTube Music. The thing is, there were some limitations to YouTube Music that made it slightly less attractive to subscribers.
One of those limitations was that unless you paid for a subscription, you would not be able to cast music from your own library to a smart speaker. That sucks for many users. However, word is that there are some changes in the YouTube Music APK that suggest that Google is removing those restrictions.
One of the features of Google Play Music was the ability to create a library of your own uploaded songs that you could access anytime, anywhere. YouTube Music does have a similar feature, but before this, users were not able to stream songs from their library to a smart speaker unless you were a paid subscriber.
The changes in the APK suggest that Google has now removed those restrictions. You’ll still need an active and paid YouTube Music subscription to continue to stream songs from YouTube Music, but if you only want to listen to your own library and cast it to a smart speaker, you should have no problem doing so.