They make their own emulators they have on the switch that you get free access to with a Nintendo online and online plus membership. They don't have wii and GameCube titles but they have nes, snes, n64, gameboy and gameboy advance.

edit: i dont know why yall are downvoting me for simply sharing what nintendo is doing. why would they put their emulators on steam if they want people to use their system? nintendo has never made their games cross-platform before. i said it's free bc people don't get Online to play the emulators probably, they get it to play their games online. also it's $20 a year, come on.