chromium/chrome/test/data/extensions/browsertest/page_action_popup/manifest.json

{
  "name": "PageAction Test",
  "manifest_version": 3,
  "version": "1.0",
  "page_action": {
    "default_icon": "icon.png",
    "default_title": "MyExtensionActionTitle",
    "popup": "a_popup.html"
  }
}