Purview-Retention Policy for Private channels

Historically, the compliance copies of private channel messages were stored in a hidden folder within the user's mailbox, which is why the scope of the Private Channel retention policy was targeted at user mailboxes. Now, private channel messages are being migrated to a hidden folder in the team's group mailbox, so they will be stored alongside the compliance data for general and shared channels. This means that any Teams channel retention policies scoped to group mailboxes will apply to all data from general, private, and shared channels within Teams for groups covered by the policy. There is no way to specify a policy to include or exclude specific channel types because the scope is defined at the group mailbox level. See Learn about retention for Teams | Microsoft Learn