@jhb You can have the Device registration with Azure AD without having Intune license. Intune license is only required when you need to use the Compliant device parameter in conditional access (compliance parameter is set by Intune Service).
Now under the New feature in Conditional access for Filter for devices you have many attributes on which you can decide a Device conditions. For example Trust Type :
None of above would need an Intune license. You can certainly explore more : https://learn.microsoft.com/en-us/azure/active-directory/conditional-access/concept-condition-filters-for-devices
-----------------------------------------------------------------------------------------------------------------
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.