Sole Global Admin (personal Microsoft account) blocked by security defaults (AADSTS530035) - cannot sign in or open a support request

I created an Azure pay-as-you-go subscription with my personal Microsoft account on 2026-10-06. That account is the only Global Administrator of the tenant and the subscription Owner. Since 2026-10-14 every sign-in to the tenant fails with AADSTS530035 "Access has been blocked by security defaults": Azure portal, My Sign-ins (security info registration) and the "can't sign in" support form all show the same error, so I can't register an MFA method or open a support request.

What I tried:

• Turned on two-step verification on the Microsoft account and passed Windows Hello: still 530035.
• The tenant's only other user can sign in to the portal but has no admin role, and creating a support request needs the Support Request Contributor role.
• Phone support only pointed me back to creating a case in the Azure portal.
• On my first sign-in an Authenticator registration screen appeared; I scanned the QR code but closed the app before the last step. Since then there is no registration prompt, only 530035.

Could a Microsoft moderator please forward this to the Data Protection team for tenant access recovery? I can share the tenant ID, subscription ID, correlation IDs and proof of ownership by private message.