Azure Portal sign-in blocked by Conditional Access step-up (AADSTS50076/acrs p1) — valid TOTP rejected on 3 separate pairings, sole admin, no other path in

I'm the sole Global Admin on a personal-Microsoft-account-owned Entra tenant. Every Azure Resource Manager sign-in (Portal, az CLI) now demands a step-up claim (claims={"id_token":{"acrs":{"essential":true,"value":"p1"}}}, error AADSTS50076) that nothing satisfies:

• Three independent TOTP pairings (Microsoft Authenticator x2, Google Authenticator x1) all rejected with error 500121, despite the server showing each as "Up to date" and device clock sync confirmed correct.
• SMS to a confirmed correct number fails to send.
• Passkey/Windows Hello never actually appears as an offered step-up method - the FIDO endpoint silently falls back to the TOTP screen.
• Azure's own support-ticket flow requires signing into the Portal with the same blocked claim, so I can't even file a ticket from inside the tenant.
• There's no second admin or break-glass account to force a re-registration.

Ordinary sign-in to Outlook/account.live.com/support.microsoft.com works fine on the same account - this is specific to the Azure Resource Manager acrs/p1 authentication context. I've read the two similar reports here (5841344, 5854455) and I'm hitting the identical wall. Is there a way to clear or reset this Conditional Access authentication context state without going through the circular ticket system, or is a Data Protection phone escalation genuinely the only route?