For compression, you would open your next.config.js and set it to false:

module.exports = {
  compress: false,
}

And for minify, you would do it in your webpack.config.js:

module.exports = {
  //...
  optimization: {
    minimize: false,
  },
};

next.config.js

module.exports = (nextConfig) => {
  return {
    ...nextConfig,
    webpack(webpackConfig) {
      return {
        ...webpackConfig,
        optimization: {
          minimize: false
        }
      };
    }
  };
};

Using next@^12.0.0 will produce unminified HTML, JS, and somewhat CSS.