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
I have an Apple TV and multiple HomePods, both the mini and the original. While all of them will work for scenes the Apple TV works best for automations so I have smart plugs for all my HomePods that power then off and back on on the middle of the night to make sure the Apple TV is the main hub.