Hello Bob Yuan,
As discussed offline, you are unable to log in to the Azure Portal due to changes made to your user account’s internal/external status in Azure.
You originally signed up for the Azure tenant using your Hotmail email address (******@hotmail.com), which created an account in the format user123_hotmail#EXT#@user123hotmail.onmicrosoft.com. However, when you changed the account to an internal user, it was converted to @user123hotmail.onmicrosoft.com. As a result, whenever you tried to sign in using your original Hotmail email address (@hotmail.com), you received the AADSTS50020 error because no tenant could be found for that account.
I have shared the more details over private message. Please check and login with that UPN.
You will be able to log in again using your updated internal account email address by signing in with your password and setting up Azure MFA.
Hope this helps! Feel free to reach out for any further queries
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