Was this one answered? I'm looking for some way of setting this administratively from the console.
it's interesting that Apple have iCloud Private Relay as part of the updated MDM restrictions reference but not Hide My Email: Restrictions | Apple Developer Documentation
Maybe you could configure Custom Settings in your iOS Restrictions profile and set allowCloudPrivateRelay to false and see if it encompasses Hide My Email as well.
EDIT: Got Hide my Email mixed up with the Mail Privacy Protection (MPP) which might proxy your mail app connectivity to your SEG - I wouldn't do that with enterprise mail. But the above might still help with controlling MPP from the console.
Is anyone else struggling to manage this setting? This might be okay for BYOD/COPE devices, it's terrible for COBO devices since you may not necessarily sign into the same device and thus you will be prompted every single time.