Turns out that some Switch 2 cartridges also work with the original Switch, and things just got interesting
Something very clever is going on within those cartridges.

It's common knowledge: when you get a game for a new console, it won't work if you play it on an older device. However, in a strange twist, it seems that may not hold true with the Switch 2. We're receiving reports that some, but not all, Nintendo Switch 2 cartridges will fit in an original Switch. However, please note that the graphical fidelity will not be the same as when playing on the newer console.