Like, ever?

That would be Pokemon Red/Green/Blue, which sold an estimated 10,230,000 copies in Japan according to Nintendo. The best-selling home console game is still Super Mario Bros., which sold an estimated 6,810,000 copies. The best-selling non-Nintendo game ever in Japan is Monster Hunter Portable 3rd, which according to Famitsu sold 4,835,761 copies. For home consoles, the best-selling non-Nintendo game was Final Fantasy VII, which sold 3,937,899 copies.

The way Animal Crossing is already close to surpassing Sword/Shield in physical sales

Blue was a seperate release so it doesn't count. I think Red/Green is around 8 millions. Don't think this is going to be easy but could end up happening. AC is probably close or over 4 millions right now in only 3 weeks and the franchise is known to have incredible legs.

It will probably surpass Super Mario Bros tho.

R/B/G are all one entry hence why Nintendo counts all their shipments as one and either way it doesn't matter too much as Blue wasn't available at retail in Japan so the 10m figure is all R/G. Nintendo's official shipments would have gen one at 10m plus.

Why do you say that Blue wasn´t available at retail? Blue is a separate game like Crystal to Gold & Silver. I don´t know why the count them together though :P

Why do you say that Blue wasn´t available at retail? Blue is a separate game like Crystal to Gold & Silver. I don´t know why the count them together though :P

Because Blue wasn't available at retail it was only available via special order if you were a Corocoro subscriber you couldn't buy it in shops Blue is more a limited edition in Japan than a separate release which is why Nintendo counts them together and why Blue was sort after in Japan. Yellow is more like Crystal being a third version Blue is not really a third version it's a limited edition of R/G, in the west Blue replaced Green and was a standard edition but then that was 2 years after Japan.

Edit: It seems a retail version came around 99/2000 almost 4 years later.