“Source”:https://nintendoeverything.com/nintendo-suing-creators-of-switch-emulator-yuzu/
While it is true emulation and emulators aren’t illegal, it sounds like what happened here is the people behind Yuzu flew too close to the sun by opening a Patreon so they can make money for working on the emulator, which throws out the common argument that they “wouldn’t be profiting from piracy,” as another huge mark against Yuzu is they saw a massive surge in Patreon supporters when Tears of the Kingdom leaked pre-release, and it sounds like Nintendo has proof that indeed more than a million copies of the game we’re pirated around that time.
I feel like it really needs to be said that if you’re making an emulator or fan game then asking for money without any approval will absolutely get you in a company’s crosshairs.