Exchange Online allows users to add personal retention tags to their maiboxes through OWA settings. Some organizations don’t like this, so they can deploy user role assignment policies to block the feature. It;s something that you could consider doing if you’re preparing to switchover to Office 365 retention policies to impose the same retention regime across multiple workloads.
https://office365itpros.com/2019/09/17/exo-mailboxes-personal-retention-tags/
