wp-scripts: using --experimental-modules causes TypeError: config.plugins is not iterable when webpack.config.js is extending plugins.

[nextgenthemes]

Description

Reduced webpack.config.js. Works perfectly fine without --experimental-modules

const WebpackNotifierPlugin = require( 'webpack-notifier' );
const defaultConfig = require( '@wordpress/scripts/config/webpack.config' );

const config = defaultConfig;

config.plugins = [ ...config.plugins, new WebpackNotifierPlugin( { onlyOnError: true } ) ];

module.exports = config;

commandline:

wp-scripts build --experimental-modules --webpack-copy-php --webpack-src-dir=plugins/nextgenthemes-blocks/src --output-path=plugins/nextgenthemes-blocks/build

[webpack-cli] Failed to load '/u/websites/webpack.config.js' config
[webpack-cli] TypeError: config.plugins is not iterable
    at Object.<anonymous> (/u/websites/webpack.config.js:6:30)
    at Module._compile (node:internal/modules/cjs/loader:1368:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1426:10)
    at Module.load (node:internal/modules/cjs/loader:1205:32)
    at Module._load (node:internal/modules/cjs/loader:1021:12)
    at Module.require (node:internal/modules/cjs/loader:1230:19)
    at require (node:internal/modules/helpers:179:18)
    at WebpackCLI.tryRequireThenImport (/u/websites/node_modules/webpack-cli/lib/webpack-cli.js:223:30)
    at loadConfigByPath (/u/websites/node_modules/webpack-cli/lib/webpack-cli.js:1406:38)
    at WebpackCLI.loadConfig (/u/websites/node_modules/webpack-cli/lib/webpack-cli.js:1515:44)

Step-by-step reproduction instructions

1. use webpack.config.js to extend plugins
2. run wp-scripts

Screenshots, screen recording, code snippet

No response

Environment info

@wordpress/scripts@27.6.0

node -v
v21.7.2

npm -v
10.5.0

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes