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

{
  "name": "Extension with default side panel path",
  "version": "1.0",
  "manifest_version": 3,
  "icons": {"180": "icon.png"},
  "permissions": ["sidePanel"],
  "side_panel": {"default_path": "default_path.html"}
}