Hey,

Check: https://shortqr.com/protection/#password-protecting-your-short-links-and-qr-codes

1. Log in to your Short QR account and navigate to the link or QR code you want to protect.
2. While editing your dynamic short link, navigate to the "Protection" tab.
3. Enter a secure password in the password field.
4. Save your changes.

So to password protect a QR code you will have to link the short link to the QR code: https://shortqr.com/connect-short-link-qr-code/

— Dave