yarn add copy-webpack-plugin --dev

Ensuite à ajouter dans le fichier webpack.config.js

// webpack.config.js
const Encore = require('@symfony/webpack-encore');
const CopyPlugin = require('copy-webpack-plugin'); // à ajouter

...

Encore

...

    // à ajouter
    .addPlugin(new CopyPlugin({
        patterns: [
            { from: 'assets/images', to: 'images' },
        ]
    }))

...

;