简短回答：对于从webpack-node-externals包导入的函数，将importType选项设置为module。
与以下配置等效：

externals: [
  function ({ context, request }: any, callback: any) {
    if (/^express$/.test(request)) {
      return callback(null, 'module ' + request);
    }
    callback();
  },
],

字符串
将外部对象的默认类型指定为“模块”。Webpack将为模块中使用的外部元素生成类似import * as X from '...'的代码。
查看更多externals/#function
工作示例：
项目结构：

$ tree -L 2 -I node_modules
.
├── dist
│   └── main.js
├── package-lock.json
├── package.json
├── src
│   └── server.ts
├── tsconfig.json
└── webpack.config.ts

2 directories, 6 files

型
src/server.ts：

import express from 'express';

const app = express();

app.get('/', (request, response) => {
    response.send('Hi there');
});

app.listen(3000, () => {
    console.log('Listen on the port 3000...');
});

型
webpack.config.ts：

import path from 'path';
import { fileURLToPath } from 'url';
import webpack from 'webpack';
import nodeExternals from 'webpack-node-externals';

const __dirname = path.dirname(fileURLToPath(import.meta.url));

const config: webpack.Configuration = {
    mode: 'production',
    entry: path.resolve(__dirname, './src/server.ts'),
    externalsPresets: { node: true },
    //@ts-ignore
    externals: [nodeExternals({ importType: 'module' })],
    experiments: {
        outputModule: true,
    },
    module: {
        rules: [
            {
                loader: 'ts-loader',
                options: {
                    transpileOnly: true,
                },
                test: /\.ts(x?)$/,
            },
        ],
    },
    output: {
        filename: '[name].js',
        clean: true,
    },
    resolve: {
        extensions: ['*', '.js', '.jsx', '.json', '.ts', '.tsx'],
    },
};

export default config;

型
tsconfig.json：

{
    "compilerOptions": {
        "target": "ESNext",
        "module": "ESNext",
        "allowSyntheticDefaultImports": true,
        "esModuleInterop": true,
        "forceConsistentCasingInFileNames": true,
        "strict": true,
        "skipLibCheck": true
    }
}

型
package.json：

{
    "version": "1.0.0",
    "scripts": {
        "build": "node --loader ts-node/esm node_modules/.bin/webpack-cli"
    },
    "type": "module",
    "devDependencies": {
        "@types/express": "^4.17.17",
        "@types/webpack": "^5.28.1",
        "@types/webpack-node-externals": "^3.0.0",
        "ts-loader": "^9.4.4",
        "ts-node": "^10.9.1",
        "typescript": "^5.1.6",
        "webpack": "^5.80.0",
        "webpack-cli": "^5.0.2",
        "webpack-node-externals": "^3.0.0"
    },
    "dependencies": {
        "express": "^4.18.2"
    }
}

型
建置记录档：

$ npm run build

> @1.0.0 build /home/lindu/workspace/webpack-samples/webpack-v5/stackoverflow/75306952
> node --loader ts-node/esm node_modules/.bin/webpack-cli

(node:31537) ExperimentalWarning: --experimental-loader is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
(node:31537) ExperimentalWarning: --experimental-loader is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
asset main.js 363 bytes [emitted] [javascript module] [minimized] (name: main)
runtime modules 396 bytes 2 modules
orphan modules 42 bytes [orphan] 1 module
./src/server.ts + 1 modules 245 bytes [not cacheable] [built] [code generated]
webpack 5.88.2 compiled successfully in 293 ms

型
产出
dist/main.js：

import * as e from 'express';
var t = {
    d: (e, o) => {
        for (var r in o) t.o(o, r) && !t.o(e, r) && Object.defineProperty(e, r, { enumerable: !0, get: o[r] });
    },
    o: (e, t) => Object.prototype.hasOwnProperty.call(e, t),
};
const o = (0, ((r = { default: () => e.default }), (a = {}), t.d(a, r), a).default)();
var r, a;
o.get('/', (e, t) => {
    t.send('Hi there');
}),
    o.listen(3e3, () => {
        console.log('Listen on the port 3000...');
    });

型
运行：

$ node dist/main.js 
Listen on the port 3000...

型
节点版本：v14.21.3