36 million.
With the successor probably 6-8 months away, Switch still has time to get up to like 35.5m by the time it is replaced, and then with Japan being by far the strongest territory for the Switch this late in the game it'll likely be the main place in the world still selling the Switch with any sort of halfway real numbers in 2026, I could see it eventually stretching past 36.5m when it's all said and done, but not quite hitting 37m.
I expect, assuming no price cut, Switch sales pretty much come to a screaming halt around the world when the successor launches at just a slightly higher price point than the Switch OLED. Maybe the Lite will be a impulse buy for some people but that's about it. Japan is the only place I think will still sell much at all once the successor is out on the market, but still I don't see it doing much more than a million total once Switch is replaced.