Games to play on a 12h flight?

I’d say 12 hours is a great amount of time to get into either Breath of the Wild (if you haven’t played it yet), or else Tears of the Kingdom (if you’ve played BotW).

I got like 50h on BoTW but I never got into it
- Ah that’s a shame. What about Mario Odyssey? Another superb game with lots to do.
  
  Otherwise I guess something like the GTA Trilogy, TMNT: Cowabunga Collection.
  
  All depends what kinds of games you like though, I guess.

Hades is my vote. Short runs mean you can take breaks/naps/whatever. Great story telling if you get hooked and want to play for hours.

Something like stardew valley , golf story and sports story would suit a plane journey quite well. Although as others have stated I've never found the switch Has held my attention for that long and I prefer to just read or try and sleep on long flight.

Best of luck finding something suitable

Edited to say I've been enjoying paper Mario 64 on nso and that might be good but I can't remember if nso can be accessed offline.

Final Fantasy Pixel Remasters, BOTW/TOTK, Pokémon Violet or Legends Arceus.

I played both Violet and Arcues. About Zelda I answer in another comment. But I NEVER played a FF game. The pixel remasters is on my wishlist but it's quite expensive. Is it worth it?
- Short answer: yes. Long answer. You can buy them individually too. If you’re going to buy just one, definitely choose FF6. They aren’t related to one another at all so it doesn’t matter where you start.

War Groove, and the battery might last a decent amount of time too.

Picross if you like puzzle games.

What's your taste?

It depends on the period ahahah. I live metroidvanias, but also story driven short games. Right now I'm a little tired of open world. I played the Pikmin 4 demo and loved it, but it doesn't release in time for my flight
- Pikmin 3 is out not sure if you already played that.
  
  Luigi's mansion 3 was fun for me on a flight.
  
  I'm a big fan of civilization just bc it's turn based and I don't constantly have to pay attention to it.
  
  Crash Bandicoot could be good since it's a game pack
- I just saw that howlongtobeat.com puts oxenfree 1 around 4.5 hours for a main story playthrough, and oxenfree 2 at 6 hours. Could be a cool 1, 2 punch and knock out both games. They have great reviews and are more narrative puzzlers.
  
  I also was recommended Dan the Diver recently, but that's PC only for now, so if you have a steam deck you could do that one.
- Well, if you live metroidvania you probably already know all the good ones already.
  
  Yes, Your Grace was a fun little story-driven thing. Or go big and branch out, something like Fire Emblem could easily soak up numerous trans-continental flights. If you'll get in-flight wifi, something like Mario Maker 2 could also fit, since you've got some platforming chops. It's basically endless content.

whatever you like and have available.

Witcher 3.

Okami (old game but a good one one the switch)

Any story of season game on the switch

Rune factory 4 (story of season rpg and also made by the same guy who made the og harvest moon)

Monster hunter (you can play offline)

I really enjoyed Blue Fire. While not perfect, having fun movement upgrades really made it for me. Occasionally, it's kind of difficult to know where to go next, so grab the official walk through on pdf on your phone or computer.

I did do two 8 hour flights recently.

Even with a USB port on the chair, the switch just doesn't hold that kind of charge, plus I got bored anyways and slept half of each.

Either you're ALREADY binging a game, or I recommend getting some other lower consumption alternative. I had a much better time just playing older games on my Anbernic 353p.

You need a spare battery. Nintendo switch won't survive that long.

I would say fire emblem 3 houses.

I ended up playing Fire Emblem Awakening on the 3DS lol