Update 1.3.0 unlocked the Azure Flute event (Arceus) if you had Pokémon Legends: Arceus save data. It also restored the ability to use Surf Glitch to reach Shaymin's Flower Paradise if you hadn't downloaded Oak's Letter yet.
This guide covers how to download the official update, verify the version number, and troubleshoot if the update isn't appearing. pokemon brilliant diamond update 130 best download
If you are searching for "best download" links online to manually install update files (often seen as .nsp or .xci files), exercise extreme caution. Update 1