Many European 3DS consoles are dying, and the eShop closed permanently in March 2023. For digital preservationists, dumping their legitimate European copy into a ROM is the only way to keep playing on future hardware (like Steam Deck via Citra).
On March 27, 2023, Nintendo shut down the 3DS eShop forever. You cannot legally buy this game digitally anymore. Physical cartridges exist, but they are rare. In Europe, physical copies were published; in North America, the physical run was extremely limited. The result: The only way for a latecomer to play the official 3DS port now is to either buy a used cartridge for $100+ on eBay or sail the high seas.
For those using custom firmware (CFW) like Luma3DS, you are looking for a specific file type. The Binding Of Isaac 3ds Rom
Most of the "dead links" you find on Reddit lead to broken Mega or Google Drive links. Because Nintendo is litigious, these files are DMCA'd frequently.
Surprisingly, Repentance is available on iPad and iPhone (with controller support). It is a perfect port. If you have a Backbone or Razer Kishi controller, your phone is a better Isaac machine than a 3DS. Many European 3DS consoles are dying, and the
The only legitimate reason to hunt for the 3DS ROM today is preservation. If you own a physical cartridge and want to back it up to your SD card to save your cartridge slot, that is your legal right in some jurisdictions.
Let’s be blunt: Downloading a Binding of Isaac: Rebirth 3DS ROM from a random website is copyright infringement. Nicalis and Edmund McMillen own the code. Even if the eShop is gone, they still hold the rights. That said, the ethical calculus has shifted for many retro gamers: On March 27, 2023, Nintendo shut down the 3DS eShop forever
If you want to play Isaac on the go ethically today, you have better options: