Manually upgrade to shakapacker and running:

yarn add @babel/core @babel/plugin-transform-runtime @babel/preset-env @babel/runtime babel-loader compression-webpack-plugin pnp-webpack-plugin terser-webpack-plugin webpack webpack-assets-manifest webpack-cli webpack-merge webpack-sources webpack-dev-server

Gemfile

@@ -14,7 +14,7 @@ gem "pg"
 # Use Puma as the app server
 gem "puma"
 # Use development version of Webpacker
-gem "webpacker", '~> 6.0.0.rc.6'
+gem "shakapacker"
 
 # Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
 gem "turbolinks", "~> 5"

Gemfile.lock

@@ -65,8 +65,8 @@ GEM
     ast (2.4.2)
     bcrypt (3.1.16)
     bindex (0.8.1)
-    bootsnap (1.9.4)
-      msgpack (~> 1.0)
+    bootsnap (1.10.1)
+      msgpack (~> 1.2)
     brakeman (5.2.0)
     browser (5.3.1)
     builder (3.2.4)
@@ -107,7 +107,7 @@ GEM
     dry-core (0.7.1)
       concurrent-ruby (~> 1.0)
     dry-inflector (0.2.1)
-    dry-initializer (3.0.4)
+    dry-initializer (3.1.1)
     dry-logic (1.2.0)
       concurrent-ruby (~> 1.0)
       dry-core (~> 0.5, >= 0.5)
@@ -227,9 +227,9 @@ GEM
       actionpack (>= 5.0)
       railties (>= 5.0)
     rexml (3.2.5)
-    rubocop (1.24.1)
+    rubocop (1.25.0)
       parallel (~> 1.10)
-      parser (>= 3.0.0.0)
+      parser (>= 3.1.0.0)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
       rexml
@@ -238,7 +238,7 @@ GEM
       unicode-display_width (>= 1.4.0, < 3.0)
     rubocop-ast (1.15.1)
       parser (>= 3.0.1.1)
-    rubocop-performance (1.13.1)
+    rubocop-performance (1.13.2)
       rubocop (>= 1.7.0, < 2.0)
       rubocop-ast (>= 0.4.0)
     rubocop-rails (2.13.2)
@@ -252,6 +252,11 @@ GEM
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2)
     semantic_range (3.0.0)
+    shakapacker (6.0.0.rc.13)
+      activesupport (>= 5.2)
+      rack-proxy (>= 0.6.1)
+      railties (>= 5.2)
+      semantic_range (>= 2.3.0)
     sprockets (4.0.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
@@ -277,11 +282,6 @@ GEM
       nokogiri (~> 1.6)
       rubyzip (>= 1.3.0)
       selenium-webdriver (~> 4.0)
-    webpacker (6.0.0.rc.6)
-      activesupport (>= 5.2)
-      rack-proxy (>= 0.6.1)
-      railties (>= 5.2)
-      semantic_range (>= 2.3.0)
     websocket-driver (0.7.5)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.5)
@@ -315,11 +315,11 @@ DEPENDENCIES
   rubocop-performance
   rubocop-rails
   selenium-webdriver
+  shakapacker
   turbolinks (~> 5)
   tzinfo-data
   web-console
   webdrivers
-  webpacker (~> 6.0.0.rc.6)
 
 RUBY VERSION
    ruby 3.0.3p157

config/webpack/base.js

@@ -1,3 +1,3 @@
-const { webpackConfig } = require('@rails/webpacker')
+const { webpackConfig } = require('shakapacker')
 
 module.exports = webpackConfig

package.json

@@ -7,38 +7,49 @@
     "postinstall": "patch-package"
   },
   "dependencies": {
+    "@babel/core": "^7.16.10",
+    "@babel/plugin-transform-runtime": "^7.16.10",
+    "@babel/preset-env": "^7.16.10",
+    "@babel/runtime": "^7.16.7",
     "@fortawesome/fontawesome-free": "^5.15.4",
     "@mixtint/coreui": "^2.1.16-2",
     "@rails/actioncable": "^6.1.4-4",
     "@rails/activestorage": "^6.1.4-4",
     "@rails/ujs": "^6.1.4-4",
-    "@rails/webpacker": "^6.0.0-rc.6",
     "@stimulus/polyfills": "^2.0.0",
+    "babel-loader": "^8.2.3",
     "bootstrap": "^4.6.1",
+    "chokidar": "^3.5.2",
+    "compression-webpack-plugin": "^9.2.0",
     "core-js": "^3.19.3",
     "css-loader": "^6.5.1",
     "css-minimizer-webpack-plugin": "^3.3.1",
     "jquery": "^3.6.0",
-    "mini-css-extract-plugin": "~> 2.4.7",
+    "mini-css-extract-plugin": "~> 2.5.1",
     "patch-package": "^6.4.7",
     "perfect-scrollbar": "^1.5.3",
+    "pnp-webpack-plugin": "^1.7.0",
     "popper.js": "^1.16.1",
     "postinstall-postinstall": "^2.1.0",
     "regenerator-runtime": "^0.13.9",
     "sass": "^1.47.0",
     "sass-loader": "^12.4.0",
     "stimulus": "^2.0.0",
     "style-loader": "^3.3.1",
+    "terser-webpack-plugin": "^5.3.0",
     "turbolinks": "^5.2.0",
-    "webpack": "^5.65.0",
-    "webpack-cli": "^4.9.1"
+    "webpack": "^5.66.0",
+    "webpack-assets-manifest": "^5.1.0",
+    "webpack-cli": "^4.9.1",
+    "webpack-merge": "^5.8.0",
+    "webpack-sources": "^3.2.3"
   },
   "resolutions": {
     "chokidar": "^3.5.2"
   },
   "babel": {
     "presets": [
-      "./node_modules/@rails/webpacker/package/babel/preset.js"
+      "./node_modules/shakapacker/package/babel/preset.js"
     ]
   },
   "browserslist": [
@@ -47,6 +58,6 @@
   "devDependencies": {
     "@webpack-cli/serve": "^1.6.0",
     "typescript": "^3.9.10",
-    "webpack-dev-server": "^4.7.2"
+    "webpack-dev-server": "^4.7.3"
   }
 }