Hi @Rustu Murat DEMIRER ,
Welcome to our forum!
Please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client, what did you do and then encounter this error?
Based on my research on the error "AADSTS500200", i found an article mentioned that it may be related to Microsoft Entra, it's suggested that you could refer to it and try to troubleshooting: Error AADSTS50020 - User account from identity provider does not exist in tenant.
If it doesn't help, i will add Entra tag to better resolve your issue.
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