What username logic do you use for internal systems?

I come from companies using Google Workspace and our logic was to use email address as username to all services.

However, for Microsoft heavy companies the username is often a shortened version of firstname+lastname (potentially also with some number).

I get that one nice thing with different usernames is to protect ie brute-force login attempt as email addresses may appear publicly (compared to the secret username logic).

What is you opinion? Is it worth it and what is you username …

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