https://arstechnica.com/gadgets/2020/10/youtube-music-opens-up-google-cast-support-for-everyone/

YouTube Music is finally opening up Chromecast support to everyone. Google Music is actively winding down this month, leaving YouTube Music as Google's only music app. A major feature gap between the two services that we've been complaining about has been the restrictive Chromecast support. On Google Music, casting just worked for everyone. On YouTube Music, casting was restricted to people paying for the monthly streaming service. For the bring-your-own-music crowd, this meant if you wanted to cast music you own to speakers you own, there was no alternative but to subscribe to a streaming service you probably didn't want.

As of today, though, Google tells us casting on YouTube Music should now work for everyone. Previously, when tapping the "cast" button, unsubscribed users would get a "subscribe to YouTube Premium" pop-up box, but now YouTube Music will starting blasting tunes to our speakers with no monthly fee.