- Monster Hunter Rise: 8.09 million units (as of February 2025).
- Stardew Valley: 7.9 million units (as of December 29, 2024).
- Suika Game: 7.4 million units (as of April 11, 2024).
- Minecraft: 6.19 million units (as of March 16, 2025).
- Among Us: 3.2 million units (as of December 2020).
- Mario + Rabbids Sparks of Hope: 3 million units (by January 15, 2024).
- Xenoblade Chronicles 2: 2.70 million copies.
- Dragon Ball FighterZ: 2.43 million units.
- Human: Fall Flat: 2 million copies (as of May 2, 2024).
- Diablo III: Eternal Collection: 1.5 million units (as of February 2024).
(AI generated list)
It´s quite dificult to come up with data, apparently. But considering the total number of sold consoles, I would argue that some people picked up a third party game here and there.
Can only talk for myself, but most of my library are non-Nintendo games.