That would be one of the three killer apps on the Nintendo Switch which are from the Legend of Zelda franchise, the Animal Crossing franchise, and the Mario Kart franchise.
Currently, on Switch 2, it is it's (once again) Mario Kart.
Mario Kart has likely been the most important (or one of the most important) franchises by Nintendo since the first game on SNES. Part of the reason that Gamecube and Wii U didn't sell very well was because of unremarkable Mario Kart releases. While Mario Kart 8 is similar to Mario Kart 8DE, it is lacking an adequate multiplayer feature, and that's why people were playing a lot of Mario Kart 7 instead; you could play 8 players, and everyone had their own screen. Mario Kart 8 on Wii U failed to move people off of Mario Kart Wii and Mario Kart 7 for this reason. Mario Kart 8DE presented a bunch of new, integral, features (especially the multiplayer) that finally made that game move substantial volumes of hardware... it very quickly overtook Mario Kart 7 as the preferred game to play in the multiplayer community (at least at my office).
As I mentioned, the key feature on MK8DE is local multiplayer on the handheld mode of the Switch. Everyone gets their own screen, and you can play massive games of 8 players on BT or 12 players local with a WiFi connection available. Plus, with a WiFi connection available you can fill up extra slots with online players, which is a step up from bots... but the biggest driving factor for Mario Kart has always been its local multiplayer, ever since the SNES when it was just two people split screen.
Legend of Zelda was single handedly carrying the Switch launch, and with Mario Kart, kept it off shelves for a very long time; while Mario Odyssey launched that quarter, it was more superfluous to the maxed out hardware sales; it's unlikely they would have changed. Breath of the Wild + Mario Kart was already enough. That's the thing about Nintendo, they have so many powerful system selling games that there's a ton of overlap. Who knows how well Super Mario Odyssey could have done without Zelda or Mario Kart? We can only guess.
Animal Crossing New Horizons was the game that drove Switch to peak sales. I don't think any other game franchise would have been capable of that. The franchise had already been rising in importance, and that became clear on 3DS.
I describe myself as a little dose of toxic masculinity.
