Here a few comparisons:
Mario Kart 8 Deluxe (19.01M)
Is now the 3rd best-selling Mario Kart game (overtook MK 7 LTD 18.47 M)
Sells basically over 1M each quater. Had only one quarter where it sold less which was its 2nd quarter on the market at 820k.
3.6M copies behind MK DS and it should catch up rather soon.
Super Smash Bros Ultimate (15.71M)
Best selling single SKU of the series.
Only 2.96M behind the combined total of Smash 4 (Wii U + 3DS)
Pretty much guaranteed to take the top spot by itself.
Super Mario Odyssey (15.38M)
Ofc already the top selling 3D Mario
Ahead of New Super Mario Bros 2 and only 1.9M behind Super Mario Bros 3
The Legend of Zelda: Breath of the Wild (14.54M)
Stands on top of the Zelda franchise. Not even OoT combined with OoT 3D can beat it in sales.
Still has strong legs and will get another push right before BotW comes out.
15M is certain, 20M could become a possibility.
Super Mario Party (7.59M)
Is now in the same region as the other 2 big Mario Party titles.
1.29M behind Mario Party 8, 1.72M behind Mario Party DS
Has a good chance at becoming the best-selling entry of the franchise.
Fire Emblem: Three Houses (2.29M)
Already 2nd best seller in the series. Only Fates is ahead and the difference is just 650k.
Super Mario Maker 2 (3.93M)
Less than 100k behind the LTD numbers of the Wii U game.
Needs 3.48M to beat the Wii U and 3DS game combined.
The Legend of Zelda: Link's Awakening (3.13M)
With only 10 days of sales it's already very close to the top 10 of best selling Zeldas.
Beat Majoras Mask 3D LTD already (3.09M) and is only 700k behind the LTD of the Gameboy original. (The DX version is at 2.22M)