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Does this issue occur in the Outlook desktop client?
According to your description, it seems that you can log in normally in Outlook on the web. If it only happens in Outlook client, it is recommended that you follow the official document steps to re-add to check whether it is feasible. Add an email account to Outlook for Windows.
If the problem persists, follow the steps in this article to fix it.
Error AADSTS50020 - User account from identity provider does not exist in tenant.
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