The Hide first and last name fields in the SOAP API for site users when making API calls from within a site with nicknames setting is now retired. To secure the first and last name fields when your users make API calls, enable Enhanced Personal Information Management. Use the instructions at Manage Personal User Information Visibility for External Users to classify personal information fields.
Where: This change applies to Aura, LWR, and Visualforce sites accessed through Lightning Experience and Salesforce Classic in Enterprise, Performance, Unlimited, and Developer editions.