Change Azure login MFA

(Apologies for the incorrect tag, I really cannot see one that is relevant)

My Azure login seems to be in some kind of limbo state, hopefully someone can help me.

I log into Azure Portal with my personal Microsoft account (ending in @outlook.com), which I have a password and authenticator app set up for and can change through account.microsoft.com.

However after logging in, Azure asks for another authenticator code, which is not the same as my Microsoft one, which I remember being forced to set up upon login about a year ago. On my app, it comes up as <email>#EXT#@<email>.onmicrosoft.com.

Now this would not be a problem except I have recently changed phones and cannot find any way to set up another authenticator app in Azure.

In the Microsoft Entra admin center, I can see my account but under authentication methods but add authentication method is greyed out. Down the bottom there's a link for Access Panel profile, but that redirects to a login page that fails with error "Selected user account does not exist in tenant 'Microsoft Services' and cannot access the application ___ in that tenant. The account needs to be added as an external user in the tenant first. Please use a different account."

My hunch is that I shouldn't have a separate code as it says I'm an external user and it should just be asking for the code for my Microsoft account, but I have no idea how I'd go about fixing that.