@Kostas Backas Thanks for posting in our Q&A. From your description, did you mean that you have assigned Microsoft 365 Business Premium license to users in intune and want to manage windows 10 devices via intune? If there is anything misunderstanding, please correct me.
For this issue, we only need to assign license to users, not devices.
https://video2.skills-academy.com/en-us/mem/intune/fundamentals/licenses-assign#assign-an-intune-license-microsoft-endpoint-manager-admin-center
And each user can enroll 25 devices to intune in default. We can change the enrollment restrictions.
https://video2.skills-academy.com/en-us/mem/intune/enrollment/enrollment-restrictions-set
Hope it will help.
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