When I create an instance with the Windows 2019 AMI and attach the volume of a snapshot from a Windows 2016 instance, the new instance gets converted to Windows 2016?
I thought the OS and its dependencies were not a part of EBS volumes as mentioned here - Is the OS and dependencies stored on ebs root volumes?
Understanding terminology in AWS can be difficult! An EBS volume is
is a durable, block-level storage device that you can attach to your instances.
Think of it like a hard drive. An Amazon Machine Image or AMI is
is a template that contains a software configuration (for example, an operating system, an application server, and applications).
An EBS contains the files and code while an AMI contains the instructions. You want to use compatible EBS volumes with the AMI. If I am using Windows X on my local hardware and try to mount a drive which contains Windows Y information it could work but I would not count on it. I recommend that if you are upgrading an EBS, perform the upgrade and create a new AMI after the upgrade completes and you verify that it works as expected.