YouTube Music gets two important features: Siri support as well as a dedicated desktop web app. With the launch of iOS 13, Apple has opened Siri integration to third-party apps. YouTube Music isn't the first music streaming service to get support, though. Spotify was the first to get the feature last month.
On top of this, YouTube Music gets a new desktop web app that won't require you to be on a browser to use the service. The functionality between the app and browser will be the same. The app hasn't fully rolled out yet, so you'll have to wait a bit if it hasn't made its way to you yet.
Source: The Verge