Youtube Music :)

"Your world of music & podcasts, now on your Garmin Wearable!
Get your music & podcasts downloaded to your watch and listen on-the-go! Enjoy playlists made just for you, catch up on the latest podcast, or download your own playlists for offline playback."

Garmin Connect IQ Store:

https://apps.garmin.com/apps/b841615b-6b4c-4425-a912-377827866362