Chromecast volume controls are disabled on Android 12 due to a ‘legal issue’
9to5google.com
9to5google.com
https://www.theverge.com/platform/amp/2021/8/13/22623977/son...
For example, Sonos has patented "Method and apparatus for adjusting volume levels in a multi-zone system" and the patent shows an app where you can set volume levels for connected devices: