Hello Katiekase1,
Thank you for reaching out in Apple Support Communities. If you haven't tried yet, we recommend to restart both the Apple TV and the HomePod. This is a step that can help resolve unexpected behavior. Once this step has been performed please test and see if you can turn off your Apple TV by using Siri with your HomePod.
If needed, here's how to restart each device:
Restart HomePod or HomePod mini
1. Open the Home app on your iPhone, iPad, or Mac that's signed in with the Apple ID that you used to set up HomePod.
2. Tap or click HomePod.
3. Scroll down, or tap or click the Settings icon
and scroll down.
4. If you have two HomePod speakers set up as a stereo pair, select Restart HomePod. If your HomePod speaker is not set up as a stereo pair, select Reset HomePod, then select Restart HomePod.
If you don't see an option to restart your HomePod, unplug it from power, then plug it back in and try again.
These steps are outlined in this article: If HomePod or HomePod mini isn't responding - Apple Support
Restart Apple TV
Do any of the following:
* Press and hold both the Back
(Siri Remote 2nd generation or later) or
(Siri Remote 1st generation) and TV
buttons on the Siri Remote until the Apple TV status light blinks rapidly.
* Disconnect Apple TV from the power outlet, wait five seconds, then reconnect it.
* Open Settings
on Apple TV, go to System and select Restart.
These steps are outlined in this helpful article: Restart Apple TV - Apple Support
We look forward to hearing back from you with an update.
Kind regards.