If you are trying to play "encrypted" 3DS ROMs, your emulator will need system keys to decrypt them on the fly.
Downloading BIOS files from the internet is considered a violation of copyright law because they contain proprietary Nintendo code. The only legal method is to dump them from your own Nintendo 3DS 3DS BIOS/FIRM Files. · Issue #451 - GitHub bios file for 3dse emulator top
file to play encrypted ROMs. You can obtain these by dumping them from your own 3DS console using tools like GodMode9. System Files: If you are trying to play "encrypted" 3DS
The most reliable and legally safe method is to "dump" (copy) the firmware from your own physical Nintendo 3DS console. : A working 3DS, an SD card, and a computer. an SD card