Why does my order page say "No shipping carrier enabled"?

The Fulfilment & Tracking box only works with a courier that is enabled and can create labels. Until you have one, it shows that message.

To fix it, go to Settings → Store Settings → Shipping Setup, scroll to Shipping Carriers, tick a label-capable courier (Shiprocket, Delhivery, Blue Dart, UPS or Envia) and click Save carriers. Click Configure, enter its details, tick Enable for this store and save.

If you deliver yourself or use a courier that isn't connected, you don't need this box. Just change the order status to Shipped and click Update Status.