Installed webpack encore and configured js and css to use it.

assets/bootstrap.js

@@ -0,0 +1,11 @@
+import { startStimulusApp } from '@symfony/stimulus-bridge';
+
+// Registers Stimulus controllers from controllers.json and in the controllers/ directory
+export const app = startStimulusApp(require.context(
+    '@symfony/stimulus-bridge/lazy-controller-loader!./controllers',
+    true,
+    /\.[jt]sx?$/
+));
+
+// register any custom, 3rd party controllers here
+// app.register('some_controller_name', SomeImportedController);