Many players confuse Platinum with the 3DS titles where QR scanning is a core mechanic.
However, there are ways that players use "codes" today to unlock legendary content in Platinum. 1. The "Mystery Gift" Exploit (Modern Event Access) pokemon platinum nds qr code work
The QR code is simply a URL shortener. It downloads a save file to your smartphone . You then need to transfer that file to a computer, then to a flashcart, then to the DS. Many players confuse Platinum with the 3DS titles
Here are some resources:
Pokémon Platinum for the Nintendo DS . This feature was first introduced in Generation 7 games, such as Pokémon Sun and Moon . then to a flashcart