After scanning the QR code, use the browser's Share button, then scroll the sheet to find Add to Home Screen. You can do this before or after signing in. Safari and Chrome on iPhone work the same way — the ⋯ menu does not include this option on iOS.

1. Tap Share — the square with an arrow pointing up. On iPhone it's along the bottom of the browser (above the home bar); on iPad it's usually top-right. Tap the page once if the toolbar is hidden.
2. Scroll down on the panel that opens. Add to Home Screen is almost never on the first screen — it sits below Messages, Mail, AirDrop, and other shortcuts. Keep scrolling.
3. If you still don't see it: look for Edit Actions or Customize at the bottom of the share sheet — then enable Add to Home Screen.
4. Tap Add to Home Screen, then tap Add to confirm.