Some references :

                                                     1st week        Installed base

MARIO KART                        1,261 M         3,07 M
ARMS                                         0,422 M         3,95 M
SPLATOON                             1,131 M         4,66 M
MARIO ODYSEE                   2,149 M         7,09 M
SUPER MARIO PARTY       ????? M        20,40 M

Including digital? 900k-1.2M

It seems that game will have strong debut in Japan, we probably talking more than 200k sold only physical numbers in Japan alone.
We also know that game is quite popular on Amazon and on Resetera said that game had very strong launch in US (link down).

So WW for first week we probably talking somewhere around 1m sold units.


https://twitter.com/BenjiSales/status/1048586846849130496?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1048586846849130496&ref_url=https%3A%2F%2Fs9e.github.io%2Fiframe%2Ftwitter.min.html%231048586846849130496

i will go with 800k - 1mil

ayyyee saw our boy Ryng Tolu respond to that!!!

This won’t be a game to take record first weeks (outside of maybe it’s own franchise), as this will be a game which sells on legs. I’d say about 650k first week. Could already be near 2 million at the end of the year though.

What he said?

900k. It's a more casual game, so it will have mediocre first week sales but great holidays.

650k

Hopefully it does well, this game's great fun!