Hello Chris, Thank you for reaching out to Microsoft QnA Platform. I would like to confirm that Microsoft Entra ID Security Defaults requires to register for and use multifactor authentication using the Microsoft Authenticator app using notifications.
Users might use verification codes from the Microsoft Authenticator app or any third party application using OATH TOTP to generate codes but can only register using the Microsoft Authenticator app notification option.
For more details you can review following documentation link and screenshot which answers all doubts about Security Default: https://learn.microsoft.com/en-us/entra/fundamentals/security-defaults
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