When you move the EC2 instance from one account to another you can follow this procedure it’s working fine, except for one details.

https://aws.amazon.com/premiumsupport/knowledge-center/account-transfer-ec2-instance/

After Creating the snapshot, when you log into the target location and you try to create an Instance from the AMI, you need to be in the same region as the source to access the snapshot.

To validate your region look at the top right corner, on the right of you account Name the region is there. Be Sure the Region is the same for the source and the destination!