I tried but seems aws has closed the door. To connect ec2 to Lightsail via private IP I have to create a "ec2-classic VPC" in ec2. But aws has disabled "ec2-classic VPC" in all regions
From what I know is that you can peer the Lightsail (AWS-managed) VPC with your normal, default EC2 VPC via the Lightsail console. Then you launch EC2 instances in the default VPC for the transfer