The NDEFReader makeReadOnly() method allows web developers to make NFC tags permanently read-only with Web NFC.
Since we’ve shipped Web NFC in Chrome 89, developers have been asking for a way to “lock” NFC tags to prevent malicious users from overwriting their content. See https://github.com/w3c/web-nfc/issues/558
This operation is a one-way process and cannot be reversed. Once an NFC tag has been made read-only, it can't be written anymore.
Web NFC restrictions apply to makeReadOnly(): It is only available to top-level frames and secure browsing contexts (HTTPS only). Origins must first request the "nfc" permission while handling a user gesture (e.g a button click). To then make the NFC tag read-only, the web page must be visible when the user touches an NFC tag with their device. The browser uses haptic feedback to indicate a tap. Access to the NFC radio is blocked if the display is off or the device is locked. When a page is placed in the background receiving and pushing NFC content is suspended.
Some additional requirements are possible, such as a separate permission for making a NFC tag read-only since it is an irreversible change.
This small addition to the NDEFReader object does not change the overall status of Web NFC interoperability or compatibility.
Signals from other implementations (Gecko, WebKit):
Gecko: No Signal 
WebKit: No Signal 
Web / Framework developers: Positive https://twitter.com/quicksave2k/status/1465615447806681090
 Both Gecko and Webkit are unlikely to object to this feature specifically, but object to the overall Web NFC API as a whole, hence doesn't make sense to bug them with specific questions on this.
This feature can't be polyfilled. It should be fairly trivial for developers to adopt this new feature.
Exposing DevTools debugging support for device-access APIs (Web NFC included) is discussed at https://bugs.chromium.org/p/chromium/issues/detail?id=1142566. For now, affordable NFC tags are required to debug Web NFC.
Yes. This feature will be fully tested at https://wpt.fyi/results/web-nfc
True if there’s new UI added. It’s not clear yet if that’s needed though.
No milestones specified