@AC Gel Thanks for posting in our Q&A.
For enable co-management for intune managed devices, I have done some research. In the official article, I find that the method in the following article will make it. However, it seems not a simple way.
https://learn.microsoft.com/en-us/mem/configmgr/comanage/tutorial-co-manage-new-devices#enable-co-management-in-configuration-manager
For dynamic group, the following link lists the rules for devices in dynamic group.
https://learn.microsoft.com/en-us/azure/active-directory/enterprise-users/groups-dynamic-membership#rules-for-devices
Currently, there is no such feature to create a dynamic group of device that are managed by Intune only. If you are interested in this feature, please post our detailed request in intune uservoice. This is a place to collect customers' requirements and problems.
https://microsoftintune.uservoice.com/forums/291681-ideas
Hope the above information will help.
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