eDiscovery search for Teams chat for on premises user now on by default

Microsoft has confirmed to me that they have now enabled by default the creation of the shadow Exchange online mailboxes to store the Teams 1:1 and 1:N compliance records. Previously this had to be a request to Microsoft to enable this feature.

Therefore with this feature on by default. How does that impact users that do not have Exchange hybrid deployment, and they have NOT synchronized their on-premises Exchange schema to Azure Active Directory.

In the Microsoft documents article https://docs.microsoft.com/en-gb/microsoft-365/compliance/search-cloud-based-mailboxes-for-on-premises-users?view=o365-worldwide it states

If your organization doesn't have an Exchange hybrid deployment, you must synchronize your on-premises Exchange schema to Azure Active Directory. If you don't do this, you might risk creating duplicate cloud-based mailboxes in Exchange Online for users that have a mailbox in your on-premises Exchange organization.

Are they at risk of creating duplicate cloud mailboxes? If so what can be done to identify if duplicate mailboxes have been created and is there any way to mitigate this?