Hi @Byeongjin Kang
Thank you for posting your query on Microsoft Q&A.
I understand that you are trying to access azure portal and encountering error "AADSTS16000".
Whenever you sign in Azure portal using Microsoft Personal Account by default you are getting connected to the Microsoft Services tenant. 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.
If you 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.
You will receive an invite email once you are added to an azure tenant and accept it, you can use https://portal.azure.com/#create/Microsoft.AzureActiveDirectory URL to create your own tenant as well.
Hope this helps. Do let us know if you have any further queries.
If this answers your query, do click `Accept Answer`
and `Yes`
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Thanks,
B. Siri Chandana.