Take a look at
https://cookbook.nodered.org/http/create-an-http-endpoint
where Node-RED builds a webpage, no html on disk.
If you want to serve a file from disk it gets a little more complicated
https://cookbook.nodered.org/http/serve-a-local-file
But you will also need to specify in the Node-RED settings file where the root of your web data is stored see How to enable ability to input local image files in to node red dashboard
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