Simple question - is it possible to create a AWS Lambda function - with no code? Essentially I am looking to create a placeholder function, but without a body.

Without any code at all, not really. But just some hello world-esque code is easy enough. I do it all the time when initially setting up a new service, you can do it a few ways. Either just a short string of the code, a virtually empty zip file, or an empty image. Depending on what your end deployment is planned to be. It doesn't actually have to have code logic.

Here's an example of how you could create a very basic stand-in function with in-line code: https://www.pulumi.com/registry/packages/aws/api-docs/lambda/callbackfunction/#basic-lambda-function (in-line code only works in Node.js though)