It seems that the AWS AMI for Appsmith is not longer available:
I’ve got this message on https://aws.amazon.com/marketplace/pp/prodview-mclslaty46ah4:
This version has been removed and is no longer available to new customers.
Did you guys drop the support for it?
Hey @josemando, welcome to the Appsmith Community!
The AWS AMI has been disabled because the Ubuntu version we were building with had an older Python version installed. Although Appsmith doesn’t use Python in its stack today, the AMI was disabled for security reasons. We are working with the AWS team to resolve this and get a secure AMI up again soon.
We haven’t dropped support for it. Just working with the AWS team to get it back up. 
This issue has been resolved.
Our AMI is now available at https://aws.amazon.com/marketplace/pp/prodview-mclslaty46ah4
Apologies for the inconvenience that this may have caused you.