Probably do not know enough about the system and the main selling point in order to make a fair guess. As far as I see it the Switch 2 will not exceed or even match the first switch sales. The switch had such a sick first year releasing what many consider the best game in three of their five best selling series Mario Odyssey, Zelda Breath of the Wild and Mario kart 8 Deluxe. Granted 2 of them could also be played on the WiiU, but no one had one of those.
The concept of the first Switch was to many new, that in combination with the outstanding first year got Nintendo of to a good start that I cannot see is possible to replicate on the new system. And the gaming space is also changing, particularly in the handheld market where a lot of gamers are content with playing on their smart phones.
I do think the Switch 2 will be a success, I do not think it will break 100 million unit sold.