A typical workflow:
If you find a legitimate set of MKDS QR codes (usually found on forums like GBAtemp, Reddit’s r/nds, or dedicated speedrun wikis), here is what you can typically unlock:
If you’re a purist with an unmodded DS and original cart, QR codes are useless. You’ll need a flashcart, CFW, or emulator. Nintendo never intended this, so there’s no elegant UI – you’re using third-party tools.