As outlined on Apple's developer site, the iPhone XS, XS Max, and XR models allow users to scan NFC tags without an app using a new background tag reading feature.
On iPhones that support background tag reading, the system scans for and reads NFC data without requiring users to scan tags using an app. The system displays a pop-up notification each time it reads a new tag. After the user taps the notification, the system delivers the tag data to the appropriate app. If the iPhone is locked, the system prompts the user to unlock the phone before providing the tag data to the app.
Background tag reading is designed to work only when a user's iPhone is in use in order to avoid unintentional tag reading. It also will not work if a device has not been unlocked, a core NFC reader is in session, Apple Pay Wallet is in use, the camera is in use, or Airplane mode is enabled.
The new background tagging function will allow an iPhone user to scan any NFC tag at a museum, store, or other location without first having to open up an app. Scanning an NFC tag will present a notification on the display, which can be tapped to launch an app.
Launching an app using this method requires a tap from the user, so it will not allow NFC-based methods to automatically launch apps sans user permission.
According to Apple, background NFC tag reading is a feature that's limited to the iPhone XS, XS Max, and XR. It is not supported on iPhone X and earlier models.