How to play game audio through headset?

This cannot be correct? how can it be a bug to only want to play audio through a headset and not through both headset and soundbar/speakers? you have always been able to choose the option to only play through a headset and turn off the output via speaker, since the September update you no longer can.

what possible use case would there be to play audio through both speaker and headset?

Through the Chat mixer settings.

When you plug a headset into a controller, the game audio and any chat you do is automatically goes through the headset speakers. Check the audio settings on the guide to make sure they are not low. press the Xbox button on the controller, move all the
way to cog icon, and select the audio option, from there you should be able to see the volume and mixer options for the headset.

I found this and thought it could possibly help you.
"Open up your Xbox Dashboard and go into the ‘Settings’ menu. From here, you’re going to want to select ‘Display and Sound’ and then find the ‘Volume’ option. This will open up several settings which allow you to channel game audio through your
headset, speakers or both. It’s worth noting that you can also choose where your chat audio comes through as well, under the same menus. This should allow you to adjust the game volume through your Xbox One headset." From: Twinfinite

Hello Sinkra,

We thank you for bringing this inquiry to our forums community, and understand that this concerns an inability to hear in-game sounds through your headset.

Our suggestion here, please attempt to follow our troubleshoot sound on your Xbox One console support article .

Try this out for us and then let us know the results.

Best wishes!