My Apple TV is my main hub. However, if I use Siri via my HomePod, I can't use any scenes that are in my HomeKit. This kinda sucks because the usecase that I bought the HomePod for, is to activate scenes.
I know that you can't "guide" Apple HomeKit to decide what device is your active hub, and what is your standby hub. However, by magic this is correct (Apple TV is active, Homepod is stand-by)
According to this article, it should not matter, but it does in my case... https://www.homekithelper.net/devices/hubs