With Nintendo's latest release, we now have updated figures as of Dec. 31, 2020.
The Switch's best selling games in Japan are as listed:
1. Animal Crossing: New Horizons - 9.19 million units
2. Super Smash Bros. Ultimate - 5.17 million units
3. Pokemon Sword/Shield - 4.99 million units
4. Splatoon 2 - 4.55 million
5. Mario Kart 8 Deluxe - 4.53 million units
6. Super Mario Odyssey - 2.62 million units
7. Ring Fit Adventure - 2.47 million units
8. The Legend of Zelda: Breath of the Wild - 2.37 million units (2.76 million units w/ the Wii U version included.)
9. Super Mario Party - 2.35 million units
10. Pokemon Let's Go Pikachu/Eevee - 2.15 million units
11. Super Mario Maker 2 - 1.4 million units
12. New Super Mario Bros. U Deluxe - 1.26 million units