Is it possible to make Node-RED into a windows portable app

It's definitely possible ... If you want a dashboard, you could start with the Node-Red-Electron app:

And then from there it looks like there are some config examples to make Electron portable:

If you don't care about having a UI there are a ton of examples of packaging and running a Node.js script as a portable app, or just run the portable version of Node.js configured to run node-red.