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.
Can you download a game on the same account to two switches and play them at the same time?
Can you play a single cartridge in both systems at the same time?