Depending on the business, the applications may need to authenticate with different login attributes. For example, social media applications use userId, email, or mobile number as the identifier, Internet banking applications use userId or username as the identifier, Corporate enterprise applications use email as the identifier.
In WSO2 Identity Server 6.0.0 provides the capability to use different login attributes as a productized feature. It gives users the flexibility to choose their preferred identity attribute when logging in, such as email, username, or mobile number. A privileged user in the organization can configure the list of allowed attributes that can be used as the login identifier.

Blogs:
https://medium.com/identity-beyond-borders/multi-attribute-login-with-wso2-identity-server-9f3974d9fab0
https://chathurangapriyadarshana.medium.com/multi-attribute-login-wso2-identity-server-867a9ee60ce1