"Up to eight Switch consoles can be connected in a wireless ad hoc network for local multiplayer games, and multiple players can play on each of the connected Switch consoles.[139][40][140] In the case of at least one game, Splatoon 2, ten Switch consoles can connect in the ad hoc network, though only eight can play directly while the other two can watch as spectators."
this is what the Wikipedia page says 🤔
@packetcat it's not possible to do local play and online at the same time, so wifi is a good guess, but i don’t know for certain