Webpack 4 is a popular module bundler for JavaScript applications. If you are encountering an error message indicating that Excel failed to load, there are a few things you can check to troubleshoot the issue.

1. Check if Excel is installed on your system: Make sure that Excel is installed and that it is version 2021. Excel is no longer supported, and new versions may require additional configuration or have different features.
2. Check if your project has the correct configuration: Ensure that your project has the correct configuration for Webpack 4. In your project's webpack.config.js file, make sure that the input and output options are set to the correct paths for your Excel files.
3. Check if your project has the correct import configuration: In your webpack.config.js file, make sure that the module option is set to "module" and that the import options are set to "all" for all the modules in your project.
4. Check if your project has the correct output configuration: In your webpack.config.js file, make sure that the output option is set to "module" and that the publicPath is set to "public".
5. Check if your project has the correct dev server configuration: If you are using a dev server, make sure that the dev server is configured to serve your Excel files correctly. You can check the publicPath configuration in the dev server's publicPath setting.

If you are still unable to resolve the issue, you may want to reach out to the Excel community or the Webpack community for assistance.