chromium/chrome/test/data/extensions/api_test/side_panel/with_action_onclick/manifest.json

{
  "name": "Side panel extension with action.onclick",
  "version": "1.0",
  "manifest_version": 3,
  "permissions": ["sidePanel"],
  "background": {
    "service_worker": "worker.js"
  },
  "action": {},
  "side_panel": {"default_path": "default_path.html"}
}