To understand why you cannot simply scan a QR code to get an Arceus or a Darkrai in Pokémon Platinum, it helps to look at the technology available at the time.

If you are trying to get a specific event Pokémon or item, let me know (an original DS, a 3DS, or an emulator) so I can give you the exact steps to unlock it. Share public link

The Nintendo DS and Nintendo DS Lite consoles do not have cameras. Nintendo did not introduce a console camera until the Nintendo DSi in late 2008, well after Pokémon Platinum was developed. Because the base hardware could not scan visual codes, developers at Game Freak never programmed QR code functionality into the game. 2. Generational Timeline

Can You Use QR Codes in Pokémon Platinum on Nintendo DS? Pokémon Platinum, released in 2008 for the Nintendo DS, remains one of the most beloved entries in the entire monster-collecting franchise. Decades after its launch, players still flock to the Sinnoh region to challenge Cynthia and explore the Distortion World. However, modern gaming features often spark questions among players returning to this classic. A frequent query is whether Pokémon Platinum supports NDS QR codes to unlock events, receive Mystery Gifts, or catch rare Pokémon.

Here is the direct answer: Why Pokémon Platinum Doesn't Have Built-In QR Codes