I have been trying to use a Dynamic Group to find all devices that haven't checked in for a given period (for example, all devices that haven't checked in > 90 days) so I can perform bulk actions on the group such as removing their enrolment. However it's not possible to bulk select the devices in a dynamic group to perform bulk actions as the selection box is greyed out with a tooltip message "Assigned by device filter".

This really limits the usefulness of dynamic groups; use cases such as finding all devices that are running older versions of macOS and then directly sending an update/upgrade command, or finding devices that need Remote Desktop enabled, or where certain conditions exist and you want to send a Lock command, etc.

Being able to perform actions in bulk on dynamic groups makes administering devices from the management interface much easier and for circumstances where an API call is not really needed for "dynamic" management of devices.