Confirmed that the 10.0.0 update has broken the Miracast functionality.
I found an older Roku Stick (3600X) at home and plugged it in. It was running version 9 something.
I had no issues connecting the Peloton via casting and hearing audio on several attempts (connect, confirm, power down, connect again, test, confirm, disconnect, test again, confirm), all with no issues.
The Roku Stick Auto-Updated overnight, and the same issue has occurred. Connection works, but no audio.
It takes 5 to 10 attempts to get it to connect and broadcast audio, and when it does, the Roku volume is very low. I need to make the Peloton volume as high as possible, then turn the TV up to a volume of 90 (0-100) in order to hear anything.
Was working fine on version of 9 of the software on both devices. Once it went to 10.0.0, it stopped working.