您可以使用dotenv-webpack包从.env文件加载环境变量，并在编译阶段替换代码中的process.env.TEMPLATE。require()支持动态模块路径。
例如
项目结构：

✗ tree -L 2 -I node_modules
.
├── dist
│   └── main.js
├── package-lock.json
├── package.json
├── src
│   ├── index.js
│   ├── templateA.js
│   └── templateB.js
└── webpack.config.js

webpack.config.js：

const path = require('path');
const Dotenv = require('dotenv-webpack');

module.exports = {
    mode: 'development',
    entry: './src/index.js',
    output: {
        path: path.resolve(__dirname, 'dist'),
        clean: true,
    },
    plugins: [new Dotenv()],
};

src/index.js：

const { name } = require(`./${process.env.TEMPLATE}`);

console.log(name);

src/templateA.js：

const name = 'template a';

export { name };

src/templateB.js：

const name = 'template b';

export { name };

构建日志：

> webpack

asset main.js 3.95 KiB [compared for emit] (name: main)
runtime modules 670 bytes 3 modules
cacheable modules 120 bytes
  ./src/index.js 75 bytes [built] [code generated]
  ./src/templateB.js 45 bytes [built] [code generated]
webpack 5.88.2 compiled successfully in 51 m

输出
dist/main.js：

/*
 * ATTENTION: The "eval" devtool has been used (maybe by default in mode: "development").
 * This devtool is neither made for production nor for readable output files.
 * It uses "eval()" calls to create a separate source file in the browser devtools.
 * If you are trying to read the output file, select a different devtool (https://webpack.js.org/configuration/devtool/)
 * or disable the default devtool with "devtool: false".
 * If you are looking for production-ready output files, see mode: "production" (https://webpack.js.org/configuration/mode/).
 */
/******/ (() => { // webpackBootstrap
/******/    var __webpack_modules__ = ({

/***/ "./src/index.js":
/*!**********************!*\
  !*** ./src/index.js ***!
  \**********************/
/***/ ((__unused_webpack_module, __unused_webpack_exports, __webpack_require__) => {

eval("const { name } = __webpack_require__(/*! ./templateB */ \"./src/templateB.js\");\n\nconsole.log(name);\n\n\n//# sourceURL=webpack:///./src/index.js?");

/***/ }),

/***/ "./src/templateB.js":
/*!**************************!*\
  !*** ./src/templateB.js ***!
  \**************************/
/***/ ((__unused_webpack_module, __webpack_exports__, __webpack_require__) => {

"use strict";
eval("__webpack_require__.r(__webpack_exports__);\n/* harmony export */ __webpack_require__.d(__webpack_exports__, {\n/* harmony export */   name: () => (/* binding */ name)\n/* harmony export */ });\nconst name = 'template b';\n\n\n\n\n//# sourceURL=webpack:///./src/templateB.js?");

/***/ })

/******/    });
/************************************************************************/
/******/    // The module cache
/******/    var __webpack_module_cache__ = {};
/******/    
/******/    // The require function
/******/    function __webpack_require__(moduleId) {
/******/        // Check if module is in cache
/******/        var cachedModule = __webpack_module_cache__[moduleId];
/******/        if (cachedModule !== undefined) {
/******/            return cachedModule.exports;
/******/        }
/******/        // Create a new module (and put it into the cache)
/******/        var module = __webpack_module_cache__[moduleId] = {
/******/            // no module.id needed
/******/            // no module.loaded needed
/******/            exports: {}
/******/        };
/******/    
/******/        // Execute the module function
/******/        __webpack_modules__[moduleId](module, module.exports, __webpack_require__);
/******/    
/******/        // Return the exports of the module
/******/        return module.exports;
/******/    }
/******/    
/************************************************************************/
/******/    /* webpack/runtime/define property getters */
/******/    (() => {
/******/        // define getter functions for harmony exports
/******/        __webpack_require__.d = (exports, definition) => {
/******/            for(var key in definition) {
/******/                if(__webpack_require__.o(definition, key) && !__webpack_require__.o(exports, key)) {
/******/                    Object.defineProperty(exports, key, { enumerable: true, get: definition[key] });
/******/                }
/******/            }
/******/        };
/******/    })();
/******/    
/******/    /* webpack/runtime/hasOwnProperty shorthand */
/******/    (() => {
/******/        __webpack_require__.o = (obj, prop) => (Object.prototype.hasOwnProperty.call(obj, prop))
/******/    })();
/******/    
/******/    /* webpack/runtime/make namespace object */
/******/    (() => {
/******/        // define __esModule on exports
/******/        __webpack_require__.r = (exports) => {
/******/            if(typeof Symbol !== 'undefined' && Symbol.toStringTag) {
/******/                Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
/******/            }
/******/            Object.defineProperty(exports, '__esModule', { value: true });
/******/        };
/******/    })();
/******/    
/************************************************************************/
/******/    
/******/    // startup
/******/    // Load entry module and return exports
/******/    // This entry module can't be inlined because the eval devtool is used.
/******/    var __webpack_exports__ = __webpack_require__("./src/index.js");
/******/    
/******/ })()
;