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.
Yes/No. Both Sony and Microsoft have quality control processes to ensure that whatever is published is going to play on first entry of the disc.
That said, publishers use A LOT of workarounds. Day 1 patches to “finish” the game. Download code inserts. And as of recent, mandatory online server check-ins. As far as I’m aware, Nintendo is the only one who allows publishing half the product with required download.