We have a private event on Friday. Can I block the booking page for that night?

Not for one night on its own. The booking page does not read your hours or count covers; it records what the guest asks for and shows it to you, so a Friday booking would still land on Orders → Reservations & waitlist for you to cancel with a message. The only way to remove the Book a table button is to switch all your tables off under Settings → Tables & QR ordering, which also stops QR ordering for that time. Most restaurants simply cancel the odd booking and tell the guest. The Tables, tabs and the kitchen screen tab in the docs explains how the booking page works.