next start starts the application in production mode. The application should be compiled with next build first.
The application will start at http://localhost:3000 by default. The default port can be changed with -p, like so:
npx next start -p 4000
Or using the PORT environment variable:
PORT=4000 npx next start
Note: PORT can not be set in .env as booting up the HTTP server happens before any other code is initialized.