Moving Lightsail from one AWS account to another.

Moving a Lightsail instance from one AWS account to another is not a straightforward process, as Lightsail instances cannot be directly transferred between accounts. However, there is a method you can use to achieve a similar result:

1. Create a snapshot of your Lightsail instance in the source account.

2. Export the Lightsail snapshot to an Amazon Machine Image (AMI) and an encrypted snapshot of an Amazon EBS volume.

3. By default, the snapshot is encrypted with an AWS managed key, which cannot be shared between accounts. To address this, you need to manually encrypt a copy of the AMI with a customer managed key that can be used from the target account.

4. Share the copied AMI with the target AWS account.

5. In the target account, launch a new EC2 instance using the shared AMI.

This process effectively migrates your Lightsail instance to an EC2 instance in the target account. It's important to note that while this method preserves your data and configuration, you'll be moving from a Lightsail environment to an EC2 environment, which may have some differences in management and pricing.

Keep in mind that you'll need to reconfigure any Lightsail-specific settings or features in the new EC2 environment. Also, ensure that you have the necessary permissions in both accounts to perform these actions.

If you require maintaining the instance within the Lightsail environment, unfortunately, there isn't a direct way to move it between accounts while keeping it as a Lightsail instance. In such cases, you might need to recreate the instance in the new account and manually transfer your data and configurations.
Sources
Resource replication or migration between AWS accounts - AWS Prescriptive Guidance
Transfer EC2 instance or AMI to another account | AWS re:Post