MFA of guest accounts should reference to the user object
The MFA information is redundant over multiple stores, if I have multiple guest accounts. It would be better if there is one place, because there is also only one valid user. If I have to update my MFA information (e.g. a new phone number), I have to open myapps.microsoft.com, switch to every directory, and provide the approbiate information. All this for guest accounts which I can use only if my user account in the default directory is valid.