Try these steps

  1. Read the permission request shown by the release version of the Mac app.
  2. Allow screen recording in the macOS settings pane opened by the app. The exact labels may vary by OS version.
  3. If you want to control your Mac with touch and pen, enable tablet input in the Mac app and allow Accessibility access.

What to check

The app can share the extended display. Tablet input also works if Accessibility is allowed.