These files can be encrypted or decrypted. Emulators like Citra typically require decrypted .3DS files to run. .CIA (CTR Importable Archive)
When discussing ROMs, it is important to address the legal landscape. Digital copyright laws vary significantly by country, but a few general principles apply globally: all 3ds roms
The Sunset of the 3DS eShop and the Importance of Preservation These files can be encrypted or decrypted
With online servers down and eShop closed: all 3ds roms