Hello Morgan, Andy,
The issue pertains to a tenant lockout, where no other global admin in the tenant has the necessary permissions to re-register MFA.
To resolve this, I have escalated to our Data Protection team through a support ticket. I see that the support ticket status is marked as resolved. Please confirm if you’re now able to log into the Azure Portal without any issues.
If all your concerns have been resolved, I would greatly appreciate it if you could mark the answer as "Accepted." This helps both us and others in the community.