Short answer: Use your profile Settings → Guestbook to choose who can post. If all toggles are off, the guestbook is disabled.
- 👤 Open Profile → Settings.
- 📖 Select Guestbook.
- ⚙️ Set who may write: everyone, friends, or no one.
- ✅ If you allow at least one group to post, the guestbook is enabled.
- 🚫 If you disable all options, no one can post (guestbook off).
💡 You can change these settings anytime.