Configure another Username than email

Hello to all.

We want to authenticate users using the link https://dev-xxxxxxxx.okta.com/api/v1/authn.
If the login is successful, the user data will be returned. However, the email address is always returned as the username. Can this be configured differently?
The user data created in the directory is used here and not, as with the access token, the data of the users registered in the application. There you can change the username from email to something else.

How can I do or configure this?
Is there any other link for this other than the one mentioned above?