@Javier M Thanks for posting in our Q&A.
Automatic MDM enrollment is just configured in "Microsoft Intune", not in "Microsoft Intune Enrollment".
Honestly, there is no method to enroll existing Azure AD joined device to intune automatically. It is suggested to remove these devices in Azure AD portal and re-enroll them to intune. I have noticed that you want to bulk enroll devices to intune. Hope the following article will help you:
Thanks for your understanding.
If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.