Famitsu numbers for the top 20 roughly add up to 45.7 million. So 15 million more for digital sales (one third of the physical) seems reasonable, so I believe your claim we are above 60m by now. 100m seems still a lot, but not impossible. BOTW 2 surely will get past 1 million. Pearl/Diamond and Legend Arceus will probably sell two millions each. So will Splatoon 3. So these four will replace games that are below 1M currently in the TOP 20.
The evergreens will keep on selling, so Nintendo needs to publish another big seller (mario Kart 9, Switch Sports?) and it should be possible to reach 100M with the TOP 20.