Creating an Apple Push certificate

To manage an iOS/iPadOS and macOS devices, an Apple MDM Push certificate is required for Intune to work properly with the devices

After you add the certificate to Intune, your users can enroll their devices using:

• The Company Portal app
• Apple's bulk enrolment methods like the Device Enrolment Program, Apple School Manager, or Apple Configurator

Refer to https://docs.microsoft.com/en-us/mem/intune/enrollment/apple-mdm-push-certificate-get for the steps on how to create the certificate and add one to Microsoft Intune.