I'll go with 30-32 million. It'll reach 22-23 this year, probably 26-27 by the end of 2022, probably 29-30 by the end of 2023 and then sales will slow a lot due to saturation so it won't sell that much in 2024 especially since the Switch 2 will likely come out that year and since that should be backwards compatible I expect the Switch to have low post successor sales in Japan like the DS so it'll likely stop close to the sales of that and the Gameboy. I won't be surprised if it does somewhat better than that though and overtakes the DS and the fact it has a shot of doing that is extremely impressive considering that Japan's population and most importantly young population has declined a tad in the past 10-15 years so even if it doesn't beat the DS in total sales it'll likely still beat it in sales per capita especially among young people which will still be a big achievement.