I chose 30-31M. While there are some factors that may make that number lower such as the potential lack of a major holiday title compared to years prior and the launch of the Switch Lite which might lower the 2020's YoY sales growth, and maybe the launch of the PS5 and Xbox SSX might affect Switch sales.
However, the Switch pretty much since it launched and especially in 2020 has put away any sort of doubt people had with Switch sales.
Arguments in 2017: All Nintendo Consoles sell well their first year, sales will fall off a cliff next year with no 3rd party support.
Arguments in 2018, Switch sales will fall off a cliff next year, just like the 3DS
Arguments in 2019, All the major games released for Nintendo Switch, and once next gen consoles come out Switch sales will slow down
Arguments in 2020: Switch sales are only high temporarily due to COVID-19 boost, Switch might be down YOY by the end of 2020. "u.S sAlEs wErE dOwN 1% iN jAnUaRy & fEbRuArY"
At this point, any doubts against the Switch are irrelevant for me. These doubts have been proven false time after time again. The reality is the Switch has an insane amount of demand rn and its not gonna slow down anytime soon. Nintendo increased their shipments to 25M and they're still selling out everywhere, the amount of unmet demand at this point is huge and Im sure Nintendo is saving a lot of their stock for the holiday season. Nintendo is gonna need to ship 30M+ to fulfill the amount of unmet demand rn. Even without a major holiday title Nintendo will be fine.