I take it back...

Mario Kart and Animal Crossing will cross FIFTY (50) MILLION!!!

honestly I only think two and those are AC and MK

Mario Kart and Animal Crossing are both going to be 35-40m sellers at least. I can see Smash crawling its way there if the Switch 2 doesn't drop before 2024 (and there's a third set of DLC), Pokemon Sw/Sh could do it but given their current legs I think they will likely top out at ~25-27.5m (again, assuming there's no more DLC and there's a mainline release next year to replace them). BOTW will top out at ~25m once BOTW2 comes and cuts its legs, Odyssey will finish around 22.5-23m (again, I think Odyssey 2 will come and cut its legs in 2021-22).

Future releases that could get there:
- If there's Pokemon gen 4 remakes next year with new features (like a Wild Area and the inclusion of new Pokemon etc.) I could see it possibly getting there.
- A gen IX that takes all the good things about Sw/Sh and fixes their issues could do it too.
- A Tomodachi Life game could definitely do it too given the huge audience overlap with Animal Crossing and potential memeability.

At this point it is clear MK8D and AC are gonna do over 40 million, and they should both hit 30 million by the end of this year I think.
Smash should join them in the 30 million category.
BotW miiiiight hit 30 million eventually.
No other game out right now will hit 30 million, nor will BotW2.
But I'd a completely brand new 2D Mario game could have the potential to do it, and if another new gen Pokemon game happens on Switch that REALLY ups the ante for the series then they'd have a chance too.

So two games are assured, likely a third game, possibly a fourth game, and the possibility for a future 5th and 6th game to make it as well.

Mario Kart 8 DX + AC:NH definitley.

BOTW and SSBU... possible but I'm not convinced yet.

Everything else that is currently released won't make 30m. We'll have to see if any future titles can reach that success.

DS had one, Wii four, and another one barely missed that goal, so, as NS caters for both portable and home users, and it's currently hugely successful, if Ninty will support it long enough after it sells its first 100M, 30M sellers could be six or even more.

Overwhelming: It didn’t took a year to look stupid. ;)

I think that SMO could reach 30M with a Nintendo Select-Version.

I'd say Smash is almost guaranteed at this point. Only ten million to go, doing over 1 million per non-holiday quarter. Presumably ~3.5 years until Switch is replaced. It's not gonna have a sequel cut off legs. And it will keep selling for the rest of Switch's life as one of the two premier multiplayer/party games on the system. I think Smash could go as high as 35 million - 15 million more sales with presumably roughly 15 quarters to go until Switch is replaced, give or take a couple quarters.

BotW is less assured, as we will have to see what effect BotW2 has on the original's sales. But it too is still doing over 1 million a quarter, and while I expect that to fall, it still could be over 30 million by late 2023.

Never mind. I‘m not a native speaker so I didn‘t recognize it.

Many people would have been with your old guess.

I answered 4:

BotW
AC: NH
Mario Kart 8
An eventual new and beautiful 2d Mario.

Correction: Damn, I forgot SSBU. 5 is my actual answer.