Some are full games, some are an empty cartridge with a key to download the game (which you can resell but not download if the servers go down). Some are a box with a code inside printed on a piece of paper (which gets associated to your account and you can't resell or download without servers).

There is a warning on the box for the two that don't include the playable game, but the fact that you need to know that or read the warning is a bit of a problem. And I don't particularly like the idea that Nintendo is deliberately confusing the issue to make people believe that buying the game in a box has no advantages.

I like the Switch 2 overall, but some of the weirdness they've done to make game licenses and physical games more complicated kinda sucks for reasons both intended and unintended.