My setup
rails 6.1.4


package.json
  "dependencies": {

    "@fullcalendar/core": "^5.9.0",

    "@fullcalendar/daygrid": "^5.9.0",

    "@fullcalendar/interaction": "^5.9.0",

    "@fullcalendar/timegrid": "^5.9.0",

    "@rails/actioncable": "^6.0.0",

    "@rails/activestorage": "^6.0.0",

    "@rails/ujs": "^6.0.0",

    "@rails/webpacker": "5.4.0",

    "moment": "^2.29.1",

    "preact": "^10.5.14",

    "stimulus": "^2.0.0",

    "turbolinks": "^5.2.0",

    "webpack": "^4.46.0",

    "webpack-cli": "^3.3.12"

  },

  "version": "0.1.0",

  "devDependencies": {

    "webpack-dev-server": "^3.11.2"

  }