About the "given_name" and "family_name" fields in UniversaLogin

Thank you for your help.
I would appreciate your advice on the following:

Condition: I cannot use the Costomize Login Page. (Because it will switch to ClassicLogin)
Currently, I can store data as metadata using Actions’ Pre User Registration.
It seems that POST /api/v2/users can use two fields, “given_name”: “string” and “family_name”: “string”,
so I would like to know how to make them usable.