Switch 2's Game-key Cards will not be account bound upon use, Nintendo confirms.

Nintendo Switch 2 will have a more formalized version of its predecessor's code-in-a-box format called Game-key Cards. These are cartridges that don't have the game on them but instead have a key to unlock a digital download of the game. Now Nintendo has clarified that these Game-key Cards work like any other cartridge, meaning they can be shared with friends and presumably sold second-hand.
"So key cards will start up on the console or system that it is slotted into, so it's not tied to an account or anything," Nintendo's Tetsuya Sasaki told GameSpot. Sasaki worked primarily on the Switch 2's system software environment.
Users had previously been worried that any games they downloaded via a Game-key Card would be redeemed and permanently tied to their account. That's not the case. Game-key Cards will function in the same way that certain Switch 1 cartridges that split a game in half; one half is on the cartridge, and the other half has to be downloaded.
This allowed publishers to keep physical software manufacturing costs down (32GB Switch 1 cartridges aren't cheap), but Game-key Cards will be even better because they are designed to effectively be empty.
The rights to the game--both download and play--are inside of the cartridge itself, not in a user's account. It's a physical version of a digital game that can be swapped and even resold.
Here's more info from the Nintendo support page:
Some physical games are available as a game-key card. Insert a game-key card to download the full game to your system. You can play the game by starting it like a standard physical game card.
Game-key cards are different from regular game cards, because they don't contain the full game data. Instead, the game-key card is your "key" to downloading the full game to your system via the internet.
After it's downloaded, you can play the game by inserting the game-key card into your system and starting it up like a standard physical game card.