Why next.js source maps are in ES5 - next.js

Question

I have set productionBrowserSourceMaps: true in next.config.js.
Full next.config.js
const { withRNV } = require('#rnv/engine-rn-next');
const path = require('path');
const fs = require('fs');
const cp = require('child_process');
const config = {
compress: false,
webpack: (cfg, { isServer }) => {
if (!isServer) cfg.resolve.alias['#sentry/node'] = '#sentry/browser';
cfg.module.rules.push({
test: /\.(eot|woff|woff2|ttf|svg|png|jpg|gif)$/,
use: {
loader: 'url-loader',
options: {
limit: 100000,
name: '[name].[ext]',
},
},
});
return cfg;
},
typescript: {
ignoreBuildErrors: true,
},
publicRuntimeConfig: {
deployEnv: process.env.DEPLOY_ENV || 'Development',
customScripts: [],
},
images: {
loader: 'akamai',
path: '',
},
async headers() {
return [
{
source: '/(.*)',
headers: [
{
key: 'X-Application-Version',
value: getPackageVersion(),
},
{
key: 'access-control-allow-origin',
value: '*',
},
],
},
];
},
experimental: {
outputStandalone: true,
},
productionBrowserSourceMaps: true,
};
module.exports = withRNV(config, {
enableNextCss: false,
enableOptimizedImages: true,
});
But in sources i see this ES5 code:
I don't see original ES6 source code.
How should I set config to see it?
This is my babel.config.js
const { withRNVBabel } = require('rnv');
const fs = require('fs');
const resolveObj = {
alias: {},
};
if (process.env.NEXT_ENV === 'prod') {
resolveObj.root = ['.'];
} else {
resolveObj.root = ['../..'];
}
const config = {
retainLines: true,
ignore: [/#babel[/\\]runtime/],
presets: ['module:babel-preset-expo'],
plugins: [
'styled-jsx/babel',
[
'module:react-native-dotenv',
{
moduleName: '#env',
path: '.env',
},
],
],
};
let finalConfig;
if (!fs.existsSync(process.env.RNV_ENGINE_PATH)) {
config.plugins.push([require.resolve('babel-plugin-module-resolver'), resolveObj]);
finalConfig = config;
} else {
finalConfig = withRNVBabel(config);
}
module.exports = finalConfig;