Last year the Switch came close to 6mil in the end. If it sells similarly from now until the end of the year as last year it would sell another 1.5mil and end up at 23.1mil.
Here's what I think the next few year could look like (assuming that the next console launches in 2024):
2022 - 4.5-5mil
2023 - 3.5mil
2024 - 2mil
And with that the Switch would be over 33mil.







