Heroku

Create a new Heroku app.

heroku create myapp

Configure Heroku to use the nodejs buildpack.

heroku buildpacks:set heroku/nodejs

Configure your app.

heroku config:set NITRO_PRESET=heroku

Ensure you have start and build commands in your package.json file.

"scripts": {
  "build": "nitro build", // or `nuxt build` if using nuxt
  "start": "node .output/server/index.mjs"
}

Add the heroku Nginx buildpack here

Change to the 'node' preset in your nitro.config

"nitro": {
   "preset":"node",
}

From the Existing app section of buildpack doc, 2 key steps are required to get things running
Step 1: Listen on a socket at 'tmp/nginx.socket' Step 2: Create a file '/tmp/app-initialized' when your app is ready to accept connections

Create custom app runner, eg: apprunner.mjs at the root of the project (or any other preferred location), in this file, create a server, using the listener generated by the node preset, then listen on the socket as detailed in the buildpack doc

import { createServer } from 'node:http'
import { listener } from './.output/server/index.mjs'

const server = createServer(listener)

server.listen('/tmp/nginx.socket') //following the buildpack doc

To create the 'tmp/app-initialized' file, use a nitro plugin, create file 'initServer.ts' at the root of the project (or any other preferred location)

import fs from "fs"

export default definePlugin((nitroApp) => {
   if((process.env.NODE_ENV || 'development') != 'development') {
      fs.openSync('/tmp/app-initialized', 'w')
   }
})

Finally, create file 'Procfile' at the root of the project, with the Procfile, we tell heroku to start nginx and use the custom apprunner.mjs to start the server
web: bin/start-nginx node apprunner.mjs

Bonus: create file 'config/nginx.conf.erb' to customize your nginx config. With the node preset, by default, static files handlers will not be generated, you can use nginx to server static files, just add the right location rule to the server block(s), or, force the node preset to generate handlers for the static files by setting serveStatic to true.