Hi vinceO，
Generally, we login the Office portal as administrator by using our admin accounts.
From your description, I notice that you mentioned the URL: https://portal.microsoftonline.com/admin/default.aspx.
I have tried to log in it with my admin account and found it’s accessible as administrator.
To narrow down the issue and address the requirement, could you please offer me more details about your requirement?
Do you mind to provide us with the URL of “the previous post” you mentioned?
Thanks,
Lawliet Xu