Nintendo doesn't have a new console this year like the PS5 or Xbox Series X and it's entirely possible that the person you're thinking about already has a Switch. (If they don't, get a Switch.)
While the previously hard-to-find Nintendo Switch is back in stock now, there are other ideas for Nintendo fans you may not have thought of. Not games, exactly (for games, just buy them an eShop gift card and let them choose), but other, more unusual ideas from the House that Mario Built.
Lego has a whole line of interactive Mario block kits timed for the 35th anniversary of Super Mario Bros. on the NES, which work with a talking Mario figure that can bop on coded blocks, turning playsets into a sort of board game. The multiple kits pair with a connected app and don't work with Nintendo Switch, but can be a whole different type of holiday game: Get the base set to make sure you have the necessary Mario figure and then add expansions.
Nintendo's Switch-connected RC car game needs a lot of room in your home, but manages to turn your indoor space into Mario Kart tracks like magic. The karts are controlled by a Nintendo Switch, turning the kart's camera feed into a video game mix of real obstacles and imaginary cars and power-ups. The Kart kit includes one car and the necessary cardboard gates, but to race a friend you'll need another Switch and another Kart and the game doesn't currently work with online players.
Nintendo does have one new handheld this year. The Game & Watch was Nintendo's original set of handhelds from way before the Game Boy and Nintendo's made a brand-new one with three games loaded. There's a perfect recreations of the NES Super Mario Bros and Super Mario Bros: The Lost Levels, plus a Game & Watch game, called Ball. It's expensive for a handheld that just plays three games, but as a collector's item and piece of nostalgia, it's brilliant.
Stuck indoors? Looking for something to get active? Nintendo's fitness accessory for the Switch arrived last year, but it's still the best workout for anyone with a Switch that docks into a TV (sorry, the Switch Lite won't work unless you buy extra Joy-Cons). The flexible Ring-Con controller and a leg strap work with a battle-adventure game that combines stretches, jogging in place, and various workout reps, plus a bunch of extra mini-game modes. Multiple family members can save their own profiles, too.
Don't sleep on the weird Labo: The cardboard-folding experiences combine elaborate papercraft with interactive games that you can play with the things you make. Making things can take hours and might require parental help, but if you're stuck inside looking for a big project to play with and have a TV-dockable Switch (not the Lite), these kits are still great. And they're often on sale. The Toy-Con Vehicle Kit (listed below) is a really fun set of driving/flying games with wheels and controllers you fold and build yourself.
OK, here's a secret about Switches: They tend to multiply. Nintendo's sneaky Switch strategy, blending family sharing with personal handheld play, means it's not crazy to consider another Switch for someone else in the same house. I've already done it and the Switch Lite ($200) might be that second system you're looking for. But keep in mind that if you're a multi-Switch household, you're better off getting physical game cartridges that can be shared.
Or, get a Switch accessory
There are tons of useful extras to get Switch owners, from controllers to docks to Bluetooth headset adapters.