@MJ, Thanks for posting in Q&A.
Based as I know, the custom notification messages target only the users in the group and are sent to each iOS/iPadOS or Android device that the user has registered. Devices in the group will be ignored when targeting the notification. Here is a link with more details.:
https://learn.microsoft.com/en-us/mem/intune/remote-actions/custom-notifications
For Android Enterprise Corporate-owned dedicated devices, just as you said, this is enrolled without user. So it will not receive the notification.
Hope the above information can help.
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