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.
Oh, I missed the UHD bit, right. Triple layer it’d cap at 20-25, yeah. Technically Switch carts were available up to 32GB, but I think like one or two games ever used that much, they were so expensive. That’s where the partial download stuff comes in.
Of course for optical media the solution was always to ship multiple discs, because the smaller discs are so cheap. Or were. With most optical media manufacturing phased out who knows how expensive optical will become.