German tech site golem.de states that google has removed the NFC unlock feature from Android:
The article mentions this as source: https://issuetracker.google.com/issues/65425413
Where a google employee mentions, that the feature was removed: "SmartLock NFC feature has been deprecated for new users. If you are not existing NFC users, the option will be hidden.". Sadly no statemany why and why it was removed so quietly.