Apple TV won’t add as hub for HomeKit
How do you get an Apple TV 4K to be added as a hub for HomeKit?
Go to the ATV Settings menu, select Airplay & Homekit and the Home Hub option is listed. Make sure it is connected (the ATV needs to be using the same Apple ID as the iPhone). It should then appear in the Home app on the iPhone.
Search Apple Support for more info on setting up a Home Hub.