Google previously announced that they would be shutting down Play Music. Subscribers who wish to continue streaming music would need to transition to YouTube Music, although there were some limitations to YouTube Music that made it slightly less attractive to would-be subscribers.
One of those limitations was that it seemed that unless you paid for a subscription, you would not be able to cast music from your own library to a smart speaker. However, according to 9toGoogle, they discovered some changes in the YouTube Music APK that suggests that Google is removing those restrictions.
For those unfamiliar, 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 has a similar feature, but before this, users were not able to stream songs from their library to a smart speaker unless you are a paid subscriber.
However, like we said, the changes in the APK suggest that Google has removed those restrictions. You will still need an active and paid YouTube Music subscription to continue to stream songs from YouTube Music, but if you just want to listen to your own library and cast it to a smart speaker, you should have no issues.