It is not possible to use a QR code for adding a withdrawal address.
A QR code is just a more visual way of representing the address.
The purpose of QR codes is to allow the easy reading of addresses. QR codes are meant for situations when it's not feasible to copy and paste the address - like when it's on a physical object like a card or poster. QR codes are also useful for mobile-to-mobile situations, when you don't want to share your contact information with the other person.
For our website to support scanning of QR codes, we'd have to require access to your webcam. We do not find this method secure enough. Thus, we do not allow adding of a withdrawal address using a QR code.
If the wallet or exchange that you plan to withdraw to is accessible from the same device as the one you sign in to Kraken from, or even if you're just able to email the address to yourself, there's no benefit in using a QR code.
Any wallet or exchange that you plan to withdraw to should give you options to view both the QR code and the address itself.
Example - finding your Coinbase deposit address:
Example - finding your Ledger Nano deposit address: