cfn generate creates node14 runtimes which isn't valid
Node14 runtimes can no longer be deployed to AWS so using cfn generate no longer creates a deployable custom resource.
However, if you update to node16, 18, 20 there is a bug within the TypeFunction container being used for cross-platform support as well. The code simply will not build if you have use-docker: true in your .rpdk-config.
Alas, if you want to bypass issues you have to use cfn generate -> update to node 16 in your template.yml and .rpdk-config -> change use-docker to false in rpdk-config as well as a few other docker settings in the config in order to build. The problem is you then use cross-platform support since you're building locally and not within the TypeFunction container (but its NodeJS so do we really care anyway?).