Hello @Luke Poyner ,
Thank you for reaching out Microsoft Q&A.
I Understand you are getting AADSTS16000: User account '{EUII Hidden}' from identity provider 'live.com' does not exist in tenant 'Microsoft Services' and cannot access the application '74658136-14ec-4630-ad9b-26e160ff0fc6'(ADIbizaUX) in that tenant. The account needs to be added as an external user in the tenant first. Sign out and sign in again with a different Azure Active Directory user account.
Whenever you sign in Azure portal using Microsoft Personal Account (Outlook, Hotmail...) you by default get connected to the Microsoft Services tenant (f8cdef31-a31e-4b4a-93e4-5f571e91255a).
You can also confirm this by navigating to Azure Active Directory > Overview blade and you can see f8cdef31-a31e-4b4a-93e4-5f571e91255a as Tenant ID.
In this default tenant, you do not have any directory associated with it which you can confirm by navigating to settings.
As this is a standard tenant without any directory associated, you cannot perform actions such as creating new users, groups, enterprise applications, and so on. To perform administrative actions, you must have administrative access to the tenant.
Solution: For this purpose, you need to create your own tenant rather than using the Microsoft Services (f8cdef31-a31e-4b4a-93e4-5f571e91255a) tenant.
To create a new tenant, open in-private/incognito browser window (just to avoid SSO), access https://azure.microsoft.com/en-us/free/ to create a free Azure account.
When you create a new tenant, you by default become the Global Administrator of the new tenant and have full access to all the options in that tenant.
If you still want to access Entra portal using your personal Microsoft account only, you can invite that user as a guest user as mentioned here : https://learn.microsoft.com/en-us/azure/active-directory/external-identities/add-users-administrator#add-guest-users-to-the-directory and assign the Global Administrator role to proceed further with the account.
Once you are added to an azure tenant and you accept the invite sent to you via email, you can use https://portal.azure.com/#create/Microsoft.AzureActiveDirectory URL to create your own tenant as well.
Hope this will help. Please "Accept the answer" if the information helped you. This will help us and others in the community as well.
Thanks & Regards
Goutam Pratti.