Hi @Kk ,
From your description, it seems that you have encountered a problem with Azure AD, please kindly understand that the Outlook tag here we mainly focus on general issues in the outlook client. It is recommended that you post a post with "Micrsoft Entra ID" tag to get more appropriate help.
According to my research, error code AADSTS700016 means that the application you are trying to sign in to is not registered with Azure AD. To resolve this issue, you need to register the application in Azure AD or contact your tenant administrator or application developer.
Here is a similar thread for your reference: https://learn.microsoft.com/en-us/answers/questions/692461/message-aadsts700016-application-with-identifier-n
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