It doesn’t matter what’s legal, it matters what you actually want to challenge in court or not.

Nintendo has shut down a romhack before (Project M - smash bros Wii mod). Even though you needed to have access to a legit copy to play it the way they tell you to on their website.

They’re even shutting down emulators that don’t include proprietary bios stuff that you’re “supposed” to rip off your own console. They shut down Nintendo Switch emulators.