The documented Approach to retaining Audit logs for User over the default 90 days is :

Manage audit log retention policies – Microsoft Purview (compliance) | Microsoft Learn

The default audit log retention policy only applies to audit records for activity performed by users who are assigned an Office 365 or Microsoft 365 E5 license or have a Microsoft 365 E5 Compliance or E5 eDiscovery and Audit add-on license. If you have non-E5 users or guest users in your organization, their corresponding audit records are retained for 90 days.

We only had a Single user for testing with a Microsoft 365 E5 license , however, confirmed that Audit Log history for ALL users was being retained over the 90 days with a 1 year retention policy being set to the tenancy.

Microsoft confirmed via s support ticket that this is a known issue as if a single user has the E5 license, it is applied tenant wide.