Take (and its modern continuations like Lime3DS ) as an example. These emulators utilize High-Level Emulation (HLE) . HLE simulates the behavior of the 3DS operating system through custom code, meaning you do not necessarily need a complete BIOS file to boot many games.
For smooth performance with Citra, consider these hardware recommendations: Nintendo 3ds Bios File Download
Downloaded files are often for the wrong region or version, leading to more headaches during setup. The Right Way: Dumping Your Own Take (and its modern continuations like Lime3DS )