This is great, but my first question is: what is the infrastructure deployed? Is this a cool resume filler, or is it a serious alternative to Vercel? Seeing something around the infra and security in the readme would be great for production grade hosting

OpenNext is just for packaging the Next.js build artifacts. The infrastructure is defined by projects that deploy those artifacts, examples here: https://opennext.js.org/aws/get_started

Some of them are, for example, Terraform projects that list the specific infra. I have experience with the SST deployment, whose website unfortunately doesn't do a great job of listing the infra architecture.