Node.js Server

Running your Next.js application as a Node.js server is the easiest way to self host Next.js with a complete feature set.
You are basically running the commands npm run build and npm run start to start your application.

The concept

The idea here is to keep the setup, and the number of tools required, as small as possible.
Node.js is directly running on your server. When your application is changing your CD environment usually does login to your server via SSH, builds the application and restarts the Node.js process.

PM2 and a Proxy

For keeping your Node.js process running (once you did close the SSH connection to the server) the tool of the trade usually is PM2.
Configure PM2 to start all your apps on server startup and you should be good to go.

This is how your PM2 ecosystem file for Next.js could look like.

module.exports = {
  apps: [
    {
      name: "nextjs",
      script: "npm",
      args: "start",
      instances: 1,
      autorestart: true,
      watch: false,
      env: {
        NODE_ENV: "production",
      },
    },
  ],
};

With this setup you can run pm2 start ecosystem.config.js to start your Next.js application.
By this point your application is running on the server but is still not properly reachable from the outside world. You still need a proxy/application server to serve your application under a given domain via port 80/443.
Popular choices are NGINX or Caddy.

Does not scale and maintain well

Having your runtime environment installed directly on your server is less than ideal.
How do you deal with upgrading the Node.js version, what do you do if you have to run another application that requires another Node.js version? Or imagine doing a OS update and a dependency of your application breaks. How do you rollback from that?
Having a dockerized application does solve all those issues and also provides you with a more consistent environment between your application stages.