Here are the most downloaded retail games. Keep in mind that many of the games were released prior to 2018.
30. Arms
29. Deemo
28. Capcom: Belt Action Collection
27. Mario + Rabbids Kingdom Battle
26. Super Bomberman R
25. Captain Toad: Treasure Tracker
24. Monster Hunter XX Nintendo Switch Ver.
23. Donkey Kong Tropical Freeze
22. Dragon Quest Builders
21. Dragon Quest Builders 2
20. Xenoblade 2
19. Rockman X Anniversary Collection
18. Bayonetta
17. 1-2-Switch
16. Fifa 18
15. Super Mario Odyssey
14. Taiko no Tatsujin: Drum ‘n’ Fun!
13. Pokémon: Let’s Go, Eevee!
12. Undertale
11. The Legend of Zelda: Breath of the Wild
10. Mario Tennis Aces
9. Minecraft
8. Pokémon: Let’s Go, Pikachu!
7. Kirby Star Allies
6. Octopath Traveler
5. Super Mario Party
4. Splatoon 2
3. Overcooked 2
2. Mario Kart 8 Deluxe
1. Super Smash Bros. Ultimate
And the download-only games:
30. Voxel Shot for Nintendo Switch
29. Ikaruga
28. The Escapists 2
27. Valkyria Chronicles for Nintendo Switch
26. Earth Wars
25. Nine Parchments
24. Rockman Classic Collection 2
23. Guns, Gore & Cannoli
22. Ultimate Chicken Horse
21. Bloodstained: Curse of the Moon
20. Gorogoa
19. Senran Kagura Reflexions
18. Detention
17. Naruto Shippuden: Ultimate Ninja Storm 3 Full Burst
16. Golf Story
15. Mom Hid My Game!
14. Snipperclips – Cut it out, together!
13. Resident Evil Revelations 2
12. Icey
11. Dead Cells
10. Wizard of Legend
9. Minna de Kuuki Yomi
8. Dragon Quest X Basic Pack
7. Arcade Archives VS. Super Mario Bros.
6. Futari de! Nyanko Daisensou
5. Hollow Knight
4. Overcooked!
3. Puyo Puyo eSports
2. Stardew Valley
1. Human Fall Flat