You simply rename a normal update file. If you try to install an encrypted update on Citra, you will get a Missing AES keys error. If you install the wrong region (e.g., a US update on a EU game), the update won't apply.

The Version 1.4 update, released to address several gameplay bugs and enhance connectivity, is the definitive version of the game.

Updating to Version 1.4 is essential for stability and compatibility with modern emulation and modified hardware. Using a decrypted CIA file for this update allows users on platforms like the Citra emulator or 3DS homebrew environments to apply necessary patches without the restrictions of standard encrypted files . Why You Need the Version 1.4 Update

Before you download anything, check your base game:

Many modern cheats and texture packs, such as the HD texture packs for Citra, require the game to be on the latest version to function correctly.