Hi,
Defender for cloud plans are not available on Management group scope, they are only available at subscription scope. This means that there is nothing that you can enable at Management Group scope for Defender for Cloud plans. If you want to configure Defender for Cloud plans on all subscriptions part of a management group you can configure Azure Policy Configure Microsoft Defender for Cloud plans at the management group scope. That way you will not have to go and configure each subscription individually, Azure Policy will do that for you by applying the policy and remediating it.
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