The Switch 2 is less a Switch than it seems?
From Nintendo's recurring "Ask The Developer" column:
It's tricky to explain... Maybe the easiest way to understand it is that the methods used to achieve compatibility between Nintendo DS and Nintendo 3DS, and between Switch and Switch 2, are completely different.
Simply put, those systems were compatible because Nintendo 3DS contained Nintendo DS hardware and Wii U contained Wii hardware. However, Switch 2 doesn't contain any Switch hardware.
Yet, Nintendo's theme for the Switch 2 – the rationale for the name – is that it really is a continuation of the Switch; not a whole new disconnected thing. Most every Switch game is supposedly compatible (each audited individually for compatibility!), plenty of flagship Switch titles are enhanced with the label "Switch 2 Edition", and even the Switch continues to receive system updates that bring its interface into synchronization with that of the Switch 2. There's a great deal that Switch users and Switch 2 users can do interactively, and it looks like that's meant to continue. This is a familiar relationship between adjacently-released consoles that Nintendo users have appreciated all the way back to the Game Boy. But it sounds like the hardware and software architecture are, apparently, more distantly compatible than any previous adjacent pair.