Is there any way to undisplay the login form on the payment screen?

No. there is no means to undisplay/ disable the login form.

Refer to the following steps as an example of actual implementation without displaying the login form:
1. Get the payment screen URL from the url of response data on Create a code.
2. Create a QR code based on the payment screen URL.
3. Display the QR code on the merchants screen with a message such as "Scan this QR code" etc.