Inbox Retention policies

Unfortunately, such configuration is not possible, as tags assigned to a given folder in the main mailbox will apply to the same folder in the Online Archive. Read for example here: https://learn.microsoft.com/en-us/exchange/security-and-compliance/messaging-records-management/retention-tags-and-policies#applying-a-retention-tag-to-a-folder-in-the-archive 

From a retention perspective, the primary mailbox and online archive should not be looked at as separate entities. Retention settings are applied to the primary mailbox, and by design, extend to the online archive. The online archive is an extension of the primary mailbox.

If you have hold (or purview retention policy) applied to the mailbox, you can preserve any items that would be deleted by such tag, though they will not be accessible via Outlook/OWA.