You have a new Microsoft 365 E5 tenant.

To create a custom trainable classifier in Microsoft Purview (formerly Microsoft Compliance Center), you must first opt into the trainable classifier feature.

Before using custom trainable classifiers, Microsoft requires manual opt-in through the Microsoft Purview compliance portal. Without this step, you cannot create a new classifier.

The Compliance Administrator role has the necessary permissions to configure data classification, DLP policies, and trainable classifiers. Global Administrator has higher privileges but is not required for this task, violating the principle of least privilege. Security Administrator is focused on security-related settings but does not manage compliance features like classifiers.