TvOS and HomePod 14.2
After the update Default Audio Output is no longer an option. It was there in the beta. Just did a factory reset and still not there. All devices are on 14.2
The Home Theater feature only works with Apple TV 4K. Previously there was an Audio Output section in Settings but that no longer exists and if you want to temporarily route audio to your HomePod you can do this using the AirPlay picker in Control Center. Just hold down the TV button on the Siri Remote to bring up Control Center.