After shutting down several popular emulators, Nintendo admits emulation is legal
(www.androidauthority.com)
Nintendo went even further than that:
https://tech4gamers.com/nintendo-linking-emulator-trafficking/
And they absolutely have said that emulation is illegal in the past:
https://www.slashgear.com/1572585/are-video-game-emulators-illegal-answer/
On their website, they name emulators in a list of "illegal activities" they want people to snitch on:
To report ROM sites, emulators, Game Copiers, Counterfeit manufacturing, or other illegal activities