Resolution when trying to run the Get Mail or Send Mail activities from the O365 Scope, there is a Pop-up that shows up which does not allow Unattended automation.
The popup is showing up because, in your Office365 app scope, you selected the auth type of Interactive token which is only suited for attended automation. To do Unattended automation, the suggestion would be to use one of the other authentication types as mentioned Unattended Vs Attended Automation.
Note: For some of the other auth types, use Application permissions in the App Registration from Azure AD as mentioned Add Permissions API - Setup.