You can set up your HomePod, Apple TV 4K, Apple TV (4th generation), or iPad as a home hub to automate and remotely control your HomeKit accessories from your iOS device. The device that you set up as a home hub must remain in your home, connected to your home Wi-Fi network, and powered on.
The HomePod automatically sets itself up as a home hub so you can control your HomeKit accessories remotely with the Home app and use automations. Just make sure that the iOS device you use to set up HomePod is signed in to iCloud with the Apple ID that you used to set up your HomeKit accessories in the Home app.
(This how-to is based on my experiences and info on Apple’s support pages — where the images sometimes come from.)