Anyone has switched DevOps organization directory from one Azure AD tenant to another for a Azure AD tenant to tenant migration scenario.
Consider an Azure AD tenant with domain xyz.co.nz (source) is being migrated to tenant with domain mnp.co.nz (target). In this case, all users will be created in target tenant and custom domain xyz.co.nz removed from source tenant and verified in target tenant. This means UPN of user accounts in source tenant will have changed to xyz.onmicrosoft.com when domain is removed.
Now if we switch directory of Azure DevOps organization that is connected to source tenant to directory of target tenant how will the users match. A user in target tenant will have email address of xyz.co.nz and an alias of mnp.co.nz whereas user within source tenant will have a UPN of xyz.onmicrosoft.com.