A decrypted ROM of (USA) for the 3DS is specifically designed for use with emulators like Citra, as these programs cannot read the original encrypted retail data.
While this version shares a name with the console/PC game, it is essentially a different title with its own unique "features" and mechanics. Key Features of the 3DS ROM Sonic Generations (Nintendo 3DS) | Sonic Wiki Zone | Fandom Sonic Generations Decrypted 3DS (USA) ROM