@Víctor Adrián Galindo Lasaosa, Thanks for posting in Q&A.
From your description, I know that you want to enroll existing Entra joined devices into Intune. Based on my research, if you want to do it in batches, it is suggested that use a provisioning package for Intune auto-enrollment.
And it is not recommended you unsubscribe from Entra ID, because it may cause losing information.
Meanwhile, please ensure the Microsoft Intune licenses and Azure AD Premium license are assigned. And the MDM user scope under Automatic enrollment is set as all.
Hope this can help you, if there is any update, feel free to contact me.
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