Apple TV 4K could not set a Single Homepod Mini as default speaker.

My iPhone is running at iOS 14.4.1, My Apple TV 4K is running at 14.4, same as my Homepod Mini.

I can manually set Homepod Mini as the Apple TV's speaker by setting in Apple TV's control panel.

I can not set Homepod Mini as the Apple TV's default speaker in TV's setting menu.

Both of my 3 devices were in the same Wi-Fi network. The TV and Homepod Mini is in the same room.

Thanks for take a look and help me out.