If you're encountering an error while trying to modify an Azure Event Grid Subscription that was automatically created by Microsoft Defender for Storage, it's likely due to resource ownership and management restrictions.

What you can do instead:

If you need a custom event handling flow (e.g., routing blob events to your own Logic App or Function App):

• Create a separate custom Event Grid Subscription manually on the same Blob Storage resource.

• This will not interfere with the Microsoft Defender subscription.