This includes several Nest Hubs, Chromecast with Google TV, and Speaker Groups in our case. You basically get the same Cast list that appears inside apps, but with icons to go with it. Google appears to be emphasizing frequently used devices by changing the colour of the device symbol.
This capability is not yet widely available. Only YouTube Music (version 5.36.51) appears in the output switcher of the apps we tested on the aforementioned Pixel 7 (with Google Play services version 22.46.17), though this app-by-app approach was expected.
