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.
Pay a premium for a physical copy of your game, and the cartridge may not contain the actual game. Only on Nintendo Switch 2.
Had a scare when first hearing this. But somewhere else on the site it does specify this as something like “some physical games”, and as quoted in OP they’re contrasting here with “regular game cards”. So it looks like real game cards will still be a thing.
So far I’ve seen screenshots of SFVI and Bravely Default boxarts marked as game-key cards.
I’ve seen box shots for Mario Kart and Donkey Kong that appear to be normal game cards.