How can you in hook up mini home pod to Apple 4K TV

1. Press and hold the Home button  on the Siri Remote to open Control Center.
2. Select the Audio Controls button .
3. A list of available audio devices appears, organized by room (as assigned in the Home app on your iOS, iPadOS, or macOS device).

You cannot use default audio setting with the minis though (from the settings app)

Use Apple TV to play audio throughout your home - Apple Support