EDIT: Cheers to Rol for the clarification; this is 23 games selling over a million during the financial year from 1st April 2018 to 31st March 2019, not lifetime.
Given the numbers we have for their first party software, (see below) that means 9 third party games sold over a million copies during that period.
[Confirmed First Party Million+ sellers for this period:
Super Smash Bros. Ultimate - 13.81m
Pokémon: Let's Go, Evee/Pikachu! - 10.63m
Mario Kart 8 Deluxe - 7.47m
Super Mario Party - 6.40m
The Legend of Zelda: Breath of the Wild - 4.30m
Super Mario Odyssey - 4.04m
New Super Mario Bros. U Deluxe - 3.31m
Splatoon 2 - 2.69m
Mario Tennis Aces - 2.64m
Donkey Kong Country: Tropical Freeze - 2.25m
Kirby Star Allies - 1.30m
Captain Toad: Treasure Tracker - 1.18m
Yoshi's Crafted World - 1.11m
Nintendo Labo Toy-Con 01: Variety Kit - 1.09m
Total: 14]Last edited by curl-6 - on 27 June 2019
Bet with Liquidlaser: I say PS5 and Xbox Series will sell more than 56 million combined by the end of 2023.