Costello posted this message on this thread today (or late yesterday, depending on your time zone):
https://gbatemp.net/threads/super-mario-3d-all-stars-rom-leaked-4-days-ahead-of-release.573679/
Just a thought from yours truly: The version released sounds like a fake. I would not download it as it could break your Switch. If you want to dump the cartridge yourself or mess with a digital copy, I suggest waiting until the game is officially launched, then you can get a
legal copy of the game which you can then do whatever you wish with it, for your own personal means. Just be aware, as Costello has already pointed out, that unofficial modifications can and will break your Switch if you're not careful.