I'm not going to explain it in details - just follow the tutorial and try to create a QR code, when hitting "save" there's the redirect.
The solution for me was to prevent the form event to bounce up.
File: app.qrcodes.$id.jsx
function handleSave(event) {
event.preventDefault(); // add this line here (and of course the arg above)
const data = {
title: formState.title,
productId: formState.productId || "",
productVariantId: formState.productVariantId || "",
productHandle: formState.productHandle || "",
destination: formState.destination,
};
submit(data, { method: "post" });
}