From https://once.com/writebook

app/javascript/controllers/dependent_checkbox_controller.js

@@ -0,0 +1,15 @@
+import { Controller } from "@hotwired/stimulus"
+
+export default class extends Controller {
+  static targets = [ "dependant", "dependee" ]
+
+  input({target}) {
+    if (target === this.dependantTarget && target.checked) {
+      this.dependeeTarget.checked = true
+    }
+
+    if (target === this.dependeeTarget && !target.checked) {
+      this.dependantTarget.checked = false
+    }
+  }
+}