The list of EC2 instances that you can protect is available in the Instances view of Veeam Backup for AWS.
Right after the product installation, the list of EC2 instances in the view is empty. Veeam Backup for AWS populates it with EC2 instances on which IAM roles that you specify in backup policy settings have permissions.
If for some reason Veeam Backup for AWS fails to update the list of EC2 instances or EC2 instance properties automatically, click Rescan at the top right corner of the Instances view.
In Veeam Backup for AWS, you can protect only EC2 instances that run in a VPC. EC2-Classic instances are not supported. For details, see this Veeam KB article.