Highlights an issue with 5.0.0-beta.29 relating to using output options:

output: {
  ...etc,
  module: true,
  libraryTarget: "module",
  libraryExport: "default",
}

with experiments:

experiments: {
  mjs: true,
  outputModule: true,
},
npm ci
npm start

This will run webpack and attempt to import the default export from the generated bundle.