Alert Hello World in UXP

Not so much jumping into the deep end but going swimming with cement flippers with UXP, I try to create an alert in InDesign .injs:

alert("hello!");

I get an alert of sorts...

But not quite as friendly as I'd hoped.

I can get around it by writing a bespoke alert function as mentioned in this recipe here.

However... it says here that Since UXP v7.4, `alert()` can only be invoked in `plugin` via the featureFlags `enableAlerts`. Update your Manifest v5 with the following:

so I've updated  the manifest:

{
  "id": "myUniqueId",
  "name": "Hello Worldplugin",
  "version": "0.0.1",
  "description": "Description goes here",
  "summary": "Summary goes here",
  "host": {
    "app": "XD",
    "minVersion": "13.0"
  },
  "uiEntryPoints": [
    {
      "type": "menu",
      "label": "Create Rectangle",
      "commandId": "createRectangle"
    }
  ],
  "featureFlags": {
     "enableAlerts": true
 }
}

based on the Developer Starter project - so ignore references to rectangles. But get the same error as above.

So what's going on?