Why is SELECT USER_NAME() returning my windows credentials and not the database user mapped to a windows security group that I am in?
If a Windows principal accessed the database by way of membership in a group, CURRENT_USER will return the name of the Windows principal instead of the group name.
https://docs.microsoft.com/en-us/sql/t-sql/functions/current-user-transact-sql?view=sql-server-ver15