You must set up a home hub to add Matter accessories to the Home app.
Thread-enabled Matter accessories require a Thread-enabled home hub, such as HomePod mini or Apple TV 4K (3rd generation) Wi-Fi + Ethernet or a supported third-party border router.
When you set up an Apple TV, HomePod or HomePod mini, it automatically becomes your home hub. To manually turn your Apple TV 4K into a home hub, go to Settings → AirPlay and HomeKit and scroll down, then select Room and choose an existing room where this Apple TV will be used or add a new one.
https://www.idownloadblog.com/2023/04/03/upgrade-smart-home-new-homekit-architecture-tutorial