The app has registered all URLs under
https://www.home-assistant.io/ios/ as valid Universal Links. However, at this time, there is only one Universal Link that the app understands:
https://www.home-assistant.io/ios/nfc/?url=<a URL you could use with the existing URL handler>
What this allows for is NFC support. You can write a NFC tag with a NDEF URL like the above and whenever your device sees that NFC tag, a notification will appear for you to open the app with.
Once you open the app, it will do whatever action you told it to in the URL.