Create a new AWS Config rule to find all VPCs that are not configured to allocate their CIDR block from an IPAM pool. Invoke an AWS Lambda function to delete these VPCs.

Create a new SCP in Organizations. Add a condition that denies the CreateVpc and AssociateVpcCidrBlock Amazon EC2 actions if the Ipv4IpamPoolId context key value is not the ID of an IPAM pool.

Create an AWS Lambda function to check for and delete all VPCs that are not configured to allocate their CIDR block from an IPAM pool. Invoke the Lambda function at regular intervals.

Create an Amazon EventBridge rule to check for AWS CloudTrail events for the CreateVpc and AssociateVpcCidrBlock Amazon EC2 actions. Use the rule to invoke an AWS Lambda function to delete all VPCs that are not configured to allocate their CIDR block from an IPAM pool.