Restoring a user to Azure API Management instance who had registered using Azure B2C

From what I've seen with Azure API Management user restoration, the "Basic" identity type is often added by default when a user resource is recreated through the ARM API, even if the original account was associated only with an external identity provider such as Azure ADB2C. This behavior appears to be tied to how APIM internally manages user entities rather than strictly mirroring the backed-up authentication configuration.

A few things you may want to verify:

Ensure that both identityProvider and identityId are being restored correctly in the request payload.

Check whether the user is being created via a PUT operation rather than imported through a backup/restore process, as APIM may apply default user settings during creation.

Review the latest API version documentation to see if there are any known changes in user identity handling.

As far as I know, there isn't a documented parameter that explicitly prevents APIM from associating the Basic identity type when recreating a user through the management API. If the additional auth type is causing issues, it may be worth opening a support ticket with Microsoft to confirm whether this is expected behavior or a platform limitation in the current API version.