Try with the Azure CLI to list all resources in the resource group to identify the hidden deployment.
az resource list --resource-group <your-resource-group-name>
Once you identify the hidden deployment, you can attempt to delete it using the Azure CLI:
az ml online-deployment delete --name <deployment-name> --resource-group <your-resource-group-name> --workspace-name <your-workspace-name>
Or you can use Azure Resource Graph Explorer to query for the deployment:
resources
| where type == "Microsoft.MachineLearningServices/workspaces/onlineEndpoints/deployments"
| where resourceGroup == "<your-resource-group-name>"
If the above steps do not work, consider opening a support ticket with Azure. They can assist in resolving resource deletion issues.
More links :
https://learn.microsoft.com/en-us/answers/questions/1529205/delete-resource-group
https://learn.microsoft.com/en-us/answers/questions/1521878/cannot-remove-resource-group