Open your emulator (e.g., Citra) and select to open the extracted game.
How to play Monster Hunter 4 Ultimate at 4K 60FPS!! (on Linux, too!)
For a visual walkthrough on configuring the emulator specifically for MH4U, check out this guide: MH4U Citra Tutorial Mr. Madness YouTube• Oct 18, 2023
Since official 3DS servers are offline, you can use alternative services like Pretendo or the emulator's built-in room system: