Hi,
Did you install other version of Office in the same PC before?
I suggest you try this method to remove the cached Office account identities from the registry:
1. Start Registry Editor.
2. Locate the following registry subkey:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Common\Identity
3. Right-click Identity, and then select Delete.
Then re-start Office application and check if this issue is still existed.
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