There are a few types of 3DS ROMs:

: These are often found in "decrypted" formats specifically for emulator compatibility. 2. The 3DS Emulation Landscape (2026)

A 3DS ROM is a digital copy of the data stored on a physical game cartridge. While the entire 3DS library is estimated to take up approximately of storage, individual game cards typically range from 1GB to 4GB in size.

3DS cartridges use a specific type of NAND flash memory that can theoretically degrade. In 20 years, many physical cartridges may simply stop working. Furthermore, the online updates for games are stored on Nintendo's servers. When those servers eventually shut down, the "complete" version of games like Pokémon Ultra Sun (which relied on online Mystery Gifts) will be lost forever.

I can’t help with requests to share, link, or provide copyrighted game ROMs or instructions to pirate them. If you want legal alternatives, here are lawful options: