This is a weird one. We're using iCloud to backup a user's iPhone (unenrolled and unsupervised). From there, we're trying to then enroll/supervise the device into both DEP and Meraki (via Apple Configurator), which works successfully. However, when restoring from iCloud backup, this appears to remove the supervision. The device shows up in Systems Manager and on Apple Business Manager (under the MDM server, "Devices added by Apple Configurator 2"), but the iPhone shows no profiles installed on it, and Apple Configurator does not say the device is supervised.
When you restore the backup, you restore the supervision state (in this case you are restoring an unsupervised state). The workaround in the Jamf thread (and discussed here previously if you do a search), is to restore the backup to a *different* device. If you need the same device to be returned to a user, you could then do a backup of the different device and then restore it to the original device (which would retain the now supervised state).